I'm 16 and have only ever built one gaming rig, so I don't have the experience to know what components are likely to be bottlenecks. This is my system, I built it two years ago and have only changed two parts since.
Motherboard: MSI K9A2 Platinum V1
CPU: AMD Phenomx4 9850 (OC'd mildly to 2.8ghz)
RAM: Patriot Viper 1066mhz (2x2gb sticks)
GPU: 2xATI 4870 512mb graphics memory (each card also has a mild factory OC)
PSU: Corsair 750 watt
I only had one graphics card in it when I bought it. I had to RMA the card about a year ago and needed the computer for school, so I bought a second card to keep my computer running until I got the first one back. When I had one card I was seeing the expected FPS rates from game benchmarks, but I didn't get too much of an improvement from adding the second card (World in Conflict only gained about 5fps on average). Because of this I believe that I'm seeing a bottleneck.
What parts are most likely the issue? I think that the CPU would be it, but I'm not sure. If the CPU is a bottleneck and I replace it with one of the more impressive phenom II's, like the 965, could my memory also be an issue? What part should be next on my list to replace, and if I need a new CPU to get everything from my graphic cards, then is my memory and motherboard good enough as is or would I have to upgrade to AM3/DDR3 to get the noticeable performance improvements? Thanks in advance for the advice.
What resolution screen do you use for gaming? Nothing is sticking out as an obvious bottleneck, except maybe the CPU.
Not all games scale well in multi-GPU setups like your 2x 4870s. Which might have been the issue with World in Conflict.
1066 DDR2 should perform near equal with 1333 DDR3 standard of AM3 boards.
So I think I agree with your guess about the CPU being the weakest link in your system.
If you look at the THG article: Best Gaming CPUs For The Money: August 2010 they have a Best Gaming CPUs For The Money: August 2010.
In the comments there they recommend that a worth while upgrade would be one that moves up three tiers or more in the chart.
You can see that a move up from your Phenom X4 9850 to a Phenom II X4 955/965 would be a 3 tier move.
And the Phenom II X4s do overclock quite a bit easier too.
Even the X6s are on that list.
I must have run across an older version of the CPU support list. You got yours off the Global site. My list was on the US site.
A google search confirms there are users out there using X4 955/965s on that board.
i wouldnt suggest any upgrades at the moment (FYI i7 X58 is the least bottleneck for SLi/Crossfire) because the new sandybridge/bulldozer is on the horizon. even if you wouldnt buy the new gen cpu+mobos you can get the current cpus/mobo for a cheaper price.
it all depends on how much are you willing to spend and when will be your next upgrade.
I think the reason you've seen little gain is because at that resolution, two 4870's are barely stretching their legs at all. Even one is almost overkill at that resolution.
That Phenom is still pretty good. Before you decide to buy a new CPU or platform, I'd try to overclock the 9850 to 3GHz; it's a bit of trouble with the Phenom X4's, but that board should be capable of doing 3GHz or beyond, providing you have proper cooling and don't set the voltages to obscene levels.
You'd likely end up with a clearer picture of what to do next, as your frames should jump up nominally if you OC successfully.
I used to have my CPU OC'd at 3ghz, but it became unstable once air temps raised during the summer. Upping the voltage to gain stability raised the temp to levels that (from what I read) AMD says will damage the unit (low to-mid 60C's under 100% usage from prime95). As far as cooling goes, I have a coolermaster Hyper212 and my case is an Antec 300 with an additional two case fans (giving me a total of two 120mm's in the front, one 120mm on the back, and a 140mm on the top).