From my personal experience it's the harddisk that plays a big role in computer bottleneck. Also the video ram and ram. Vram depends on how big your screen resolution you want to play on. Obviously GPU has to be decent to run high graphics mode if you want it all turned on. CPU isn't that important, that's from my experience , 3d games uses mostly GPU power for rendering real time pixel on screen. I have the Asus COG8580 with GTX680 on board 3G vram. 16G physical Ram. SSD for C drive and 10k RPM for games and programmes. Works fine for most games. The cpu is i7Quad 3.6Mhz if not mistaken with hyperthread so there are 8 core registered on the task manager. I am absolutely crazy about modding afterwards ... so my ASUS COG system case allow me to add more to the system as I deem fit in future. If you are willing to spend good money go for the ASUS COG they are pretty solid.
Hard disk? Bottleneck? :S
IMHO, as a rough guide:-
Regular ED gameplay: GPU > CPU > HD
For some more intensive stuff (eg: Factions): CPU > GPU > HD