I have the ATI Sapphire 5670 ddr5 512mb GPU and I am planning to get the AMD Athlon II X4 640 CPU. Will this beast of a cpu bottleneck my video card? And if it does, can't I just run the 5670 in crossfire to compensate for the cpu?
If an Athlon II X4 bottlenecked your GPU, running a 2nd one in crossfire would only further create a larger bottleneck, not fix it.
You didn't bother to mention your resolution, but a 5670 is honestly weak enough that even low res gaming the Athlon II should keep up just fine. If your gaming at 1680x1050+ than I can say for sure the 5670 will actually be your weak link in games.
I dont think you understand what a bottleneck is...Think of this in terms of BEER. If you have your athlon II (standard beer bottle) and your 5670 (funnel) adding another 5670(funnel) is not going to get the beer out of the Athlon (beer bottle) any faster. But, if you had a core i7 (fire hose of beer) into 1 5670 (funnel), the funnel will overflow and beer (data) will not go through it fast enough and the funnel will be the limiting factor ("botleneck") Increasing the size of that funnel at that stage would make sense (adding another 5670). As an exception you could also say as you make the screen resolution higher, the "funnel" gets smaller. At higher resolutions more GFX card power is needed. Hope that clears things up...