I guess this works...

osu.Game/Graphics/UserInterface/OsuSliderBar.cs

@@ -10,8 +10,6 @@ using osu.Framework.Graphics;
 using osu.Framework.Graphics.Sprites;
 using osu.Framework.Graphics.UserInterface;
 using osu.Framework.Input;
-using System;
-using System.Globalization;
 
 namespace osu.Game.Graphics.UserInterface
 {
@@ -25,20 +23,16 @@ namespace osu.Game.Graphics.UserInterface
         private readonly Box leftBox;
         private readonly Box rightBox;
 
-        public Func<T, string> TooltipTextFunc { get; set; }
+        public virtual string TooltipText
-
-        public string TooltipText
         {
             get
             {
-                if (TooltipTextFunc != null) return TooltipTextFunc(Current);
-
                 var bindableDouble = CurrentNumber as BindableNumber<double>;
                 if (bindableDouble != null)
                 {
                     if (bindableDouble.MaxValue == 1 && (bindableDouble.MinValue == 0 || bindableDouble.MinValue == -1))
                         return bindableDouble.Value.ToString(@"P0");
-                    return bindableDouble.Value.ToString(@"n1", CultureInfo.InvariantCulture);
+                    return bindableDouble.Value.ToString(@"n1");
                 }
 
                 var bindableInt = CurrentNumber as BindableNumber<int>;

osu.Game/Overlays/Options/OptionSlider.cs

@@ -6,15 +6,19 @@ using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Primitives;
 using osu.Framework.Graphics.Sprites;
+using osu.Framework.Graphics.UserInterface;
 using osu.Game.Graphics.Sprites;
 using osu.Game.Graphics.UserInterface;
-using System;
 
 namespace osu.Game.Overlays.Options
 {
-    public class OptionSlider<T> : FillFlowContainer where T : struct
+    public class OptionSlider<T> : OptionSlider<T, OsuSliderBar<T>> where T: struct
     {
-        private readonly OsuSliderBar<T> slider;
+    }
+
+    public class OptionSlider<T,U> : FillFlowContainer where T : struct where U : SliderBar<T>, new()
+    {
+        private readonly SliderBar<T> slider;
         private readonly SpriteText text;
 
         public string LabelText
@@ -38,18 +42,6 @@ namespace osu.Game.Overlays.Options
             }
         }
 
-        public Func<T,string> TooltipText
-        {
-            get
-            {
-                return slider.TooltipTextFunc;
-            }
-            set
-            {
-                slider.TooltipTextFunc = value;
-            }
-        }
-
         public OptionSlider()
         {
             RelativeSizeAxes = Axes.X;
@@ -62,7 +54,7 @@ namespace osu.Game.Overlays.Options
                 {
                     Alpha = 0,
                 },
-                slider = new OsuSliderBar<T>
+                slider = new U()
                 {
                     Margin = new MarginPadding { Top = 5, Bottom = 5 },
                     RelativeSizeAxes = Axes.X

osu.Game/Overlays/Options/Sections/Audio/OffsetOptions.cs

@@ -18,11 +18,10 @@ namespace osu.Game.Overlays.Options.Sections.Audio
         {
             Children = new Drawable[]
             {
-                new OptionSlider<double>
+                new OptionSlider<double,OffsetSlider>
                 {
                     LabelText = "Audio Offset",
                     Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.AudioOffset)
-                    TooltipText = value => value.ToString(@"0ms")
                 },
                 new OsuButton
                 {
@@ -31,5 +30,10 @@ namespace osu.Game.Overlays.Options.Sections.Audio
                 }
             };
         }
+
+        private class OffsetSlider : OsuSliderBar<double>
+        {
+            public override string TooltipText => Current.Value.ToString(@"0ms");
+        }
     }
 }

osu.Game/Overlays/Options/Sections/Gameplay/SongSelectOptions.cs

@@ -5,7 +5,7 @@ using osu.Framework.Allocation;
 using osu.Framework.Configuration;
 using osu.Framework.Graphics;
 using osu.Game.Configuration;
-using System.Globalization;
+using osu.Game.Graphics.UserInterface;
 
 namespace osu.Game.Overlays.Options.Sections.Gameplay
 {
@@ -18,20 +18,23 @@ namespace osu.Game.Overlays.Options.Sections.Gameplay
         {
             Children = new Drawable[]
             {
-                new OptionSlider<double>
+                new OptionSlider<double,StarSlider>
                 {
                     LabelText = "Display beatmaps from",
-                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.DisplayStarsMinimum),
+                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.DisplayStarsMinimum)
-                    TooltipText = value => value.ToString(@"0.## stars", CultureInfo.InvariantCulture)
                 },
-                new OptionSlider<double>
+                new OptionSlider<double,StarSlider>
                 {
                     LabelText = "up to",
-                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.DisplayStarsMaximum),
+                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.DisplayStarsMaximum)
-                    TooltipText = value => value.ToString(@"0.## stars", CultureInfo.InvariantCulture)
                 },
             };
         }
+
+        private class StarSlider : OsuSliderBar<double>
+        {
+            public override string TooltipText => Current.Value.ToString(@"0.## stars");
+        }
     }
 }
 

osu.Game/Overlays/Options/Sections/Input/MouseOptions.cs

@@ -1,7 +1,6 @@
 // Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
-using System.Globalization;
 using osu.Framework.Allocation;
 using osu.Framework.Configuration;
 using osu.Framework.Graphics;
@@ -19,11 +18,10 @@ namespace osu.Game.Overlays.Options.Sections.Input
         {
             Children = new Drawable[]
             {
-                new OptionSlider<double>
+                new OptionSlider<double,SensitivitySlider>
                 {
                     LabelText = "Sensitivity",
-                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.MouseSpeed),
+                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.MouseSpeed)
-                    TooltipText = value => value.ToString(@"0.##x", CultureInfo.InvariantCulture)
                 },
                 new OsuCheckbox
                 {
@@ -57,5 +55,10 @@ namespace osu.Game.Overlays.Options.Sections.Input
                 },
             };
         }
+
+        private class SensitivitySlider : OsuSliderBar<double>
+        {
+            public override string TooltipText => Current.Value.ToString(@"0.##x");
+        }
     }
 }

osu.Game/Overlays/Options/Sections/SkinSection.cs

@@ -8,7 +8,6 @@ using osu.Game.Configuration;
 using osu.Game.Graphics;
 using osu.Game.Graphics.UserInterface;
 using OpenTK;
-using System.Globalization;
 
 namespace osu.Game.Overlays.Options.Sections
 {
@@ -60,17 +59,15 @@ namespace osu.Game.Overlays.Options.Sections
                     LabelText = "Always use skin cursor",
                     Bindable = config.GetBindable<bool>(OsuConfig.UseSkinCursor)
                 },
-                new OptionSlider<double>
+                new OptionSlider<double,SizeSlider>
                 {
                     LabelText = "Menu cursor size",
-                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.MenuCursorSize),
+                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.MenuCursorSize)
-                    TooltipText = value => value.ToString(@"0.##x", CultureInfo.InvariantCulture)
                 },
-                new OptionSlider<double>
+                new OptionSlider<double,SizeSlider>
                 {
                     LabelText = "Gameplay cursor size",
-                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.GameplayCursorSize),
+                    Bindable = (BindableDouble)config.GetBindable<double>(OsuConfig.GameplayCursorSize)
-                    TooltipText = value => value.ToString(@"0.##x", CultureInfo.InvariantCulture)
                 },
                 new OsuCheckbox
                 {
@@ -79,5 +76,10 @@ namespace osu.Game.Overlays.Options.Sections
                 },
             };
         }
+
+        private class SizeSlider : OsuSliderBar<double>
+        {
+            public override string TooltipText => Current.Value.ToString(@"0.##x");
+        }
     }
 }