Simply take a look at the following comparison screenshot:
SharpDevelop 4.4 now supports displaying documentation for the recent .NET framework 4.5 and 4.5.1 upgrades in code completion. You can get the Developer Pack from here. SharpDevelop 4.4 nightly builds are available here.
NOTE: These changes are not yet merged into SharpDevelop 5.0. (Read: SharpDevelop 5.0 doesn't yet support the documentation for .NET 4.5 and 4.5.1.)