There is a bit of confusion as to the .NET Framework versions as opposed to the CLR (Common Language Runtime) versions.

Up until .NET Framework 2.0, the CLR versions advanced side by side with the versions of the framework.

Starting from .NET Framework v3.0, the version of the CLR stated at 2.0 (there was no significant change in the CLR itself) and the framework's version kept on going forward.

.NET Framework v3.5 actually runs on CLR 2.0 SP1.

This means that you can should be able to use the SOS.dll located at Microsoft.NET\Framework\v2.0.50727 with either Visual Studio (as I've explained on this post) or with WinDbg.

Dave Broman of Microsoft has written a post about the mapping of the versions of the .NET Framework to the version of the CLR. Do mind that as Dave states in his post, its the way he figures things up in his head and not the official documentation on this matter.