That question is coming up a lot recently. Normally I think it won't. The only real test has been this one:http://www.tweaktown.com/articles/1472/intel_p45_vs_x48_crossfire_performance/index.html
But you have to remember this uses a quad core OC'd to 4 Ghz, and the only game that really got bottlenecked at was Crysis at 1280x1024. Every other game tested was fine until you hit resolutions like 2560x1600.
But in the future (say 6 months from now) it'll probably bottleneck the new games quite a bit. If
the rest of your system can keep up (mainly the processor).
At the resolution you have now I doubt it'll bottleneck anything.