Hi Charlie,

This might seem odd, but I'd suggest using our MVC3 DLL for now because they're compatible with MVC4.
By this I mean that you can use our MVC (3) controls in an MVC4 project where you use MVC3 project features.
In the upcoming volume release (sometime this fall) we'll have an MVC4-compiled DLL as well.

However, at this time personally I cannot guarantee that our controls (and their resources - CSS and JS) will work out-of-the-box with some of the new fancy MVC4 features such as resource bundling.
(We'll have compatibility with at least one of those fancy features but it's too early for me to disclose which one)
MVC4 and the new .NET platform are still RC so we're focusing on the already released stable release (MVC3 and .NET framework 4).

I've read the RC release notes and white papers on MSDN and personally expect a lot of "gotchas" in some scenario (regardless if our controls are used or not).
Of course there could be workarounds, but I'm guessing those will come into play once more people start bumping around and ask questions/post answers. 

Also, I think that migrating to a full-blown MVC4 project will be easier once the RTM build of the new .NET Framework (and its first Service Release) seeing as how thing will be much more settled-down than with the RC build, but that's just my personal opinion.

So, I hope I've helped you with your choice and I wish you the best of luck with this new project.

Cheers!
Borislav