Okay, I want to build a new PC this fall as well and I'm also wondering what to do.
Cause you know, as my screen is only like 1280x1024, I don't really see the use of gaming in 1600x1200 (okay, that's kind of cool.) or higher. 1280x1024 with some aliasing seems fine to me. And I think qith the quadcore, I can run HL2 easily in that resolution, with all settings maxed. I'd guess same goes for BioShock/Assassins Creed, as long as you have a good GPU - which matters the most if I'm right.
So although I might not profit that much NOW, it won't be bothering me as I'm not one of those bigger resolution == better guys, while I still profit when (for example) Alan Wake comes out.
Just laying down some questions from my side

I think both processors are awesome anyway. Lots of power.