I've just finished my homebuilt system which consists of the following parts:
CPU: AMD Athlon II x4 620
Mobo: Gigabyte GA-MA790X
RAM: 2x2Gb A-data DDR2 @ 800MHz
PSU: Coolermaster @ 750W
HDD: Western Digital Blue Caviar 500GB
GFX: 2 pieces of ATI HD4870 512 Mb running in CrossfireX
OS: Windows 7 Ultimate 64-bit
I suspect a severe bottleneck. When I run 3dmark 06 with standard settings on my system, I get around 14000 points, which is well below what you could espect. When I turn CrossfireX off, I get around 11700 points. So there's only a 2000 points gain. Also, I bought the GFX from a friend who had a similar system with a Intel Qxxxx quadcore CPU and got around 20 000 points. Also he could run the newest games, for example battlefield bad company 2 on highest settings in high resolution. I can barely run BFBC2 on medium.
The most likely bottleneck I find is the CPU. Though there's a problem with that theory. When I check benchmarks where they have tried the same system with different CPU:s it only differs on maybe a 1000 - 2000 points in 3dmark 06 between the Athlon II x4 620 and the Phenom II x4:s and some of the intel i7:s. Correct me if I'm wrong, but that's what I could interpret from some of the benchmarks. But still, the CPU is the most probable bottlenek. Or?
I would be deeply thankful for all the help I could get. I just upgraded my system and kept the CD/DVD, HDD and processor but bought the rest. Which costed some money of course. And it was in purpose to be able to play new games. Which I should be able to. So please: is there a possible solution to the problem? May I gain a lot of performance by changing the CPU?
What resolution are you gaming at? Make sure you have the latest drivers from ATI. Also, run some benchmarks on a game (not 3dmark 06) at different resolutions. If you have a CPU bottleneck, there won't be much of a drop between resolutions. Refer to todays SBM article where they used a dual core i3 with 2 gtx460's for what bottlenecked results will look like.
You didn't mention if you had overclocked the processor or not. If you haven't but are open to it, try that and see if that changes your results. If it is a CPU bottleneck, overclocking your processor will show a definite improvement. The processor you choose does seem rather anemic for a crossfire 4870 setup.