What is the fastest gaming PC I can build around $1100?

Do not go with a core i7 for gaming if that is all you wish to do, a core i7 will perform just as well as a core 2 duo, the reason is because in gaming the graphics card does all of the heavy lifting in terms of computational use. If I were you I would try to at least get something like a GTX 260 (core 216) as you will only pay a little bit more and the performance increase will be fairly noticeable. But to reiterate, A HIGH END CPU IS NOT NECESSARY FOR FAST GAMES! A HIGH END GPU IS A MUST THOUGH!