Based on your system, I would have to agree with the folks from the Storage forum that your HDD is you bottleneck. You are running good memory speeds for the LGA 775 socket. Without knowing your timings, you might be able to get a slight improvement by getting lower CAS memory but won't effect the system as much as a new hard drive or SSD.
Thanks for the reply
My system used to run a lot faster, but recently it has become very slow. First I thought it was my OS that needed a reinstall - but that didn't help. I have just tried a brand new HDD but that didn't help either. I have tried installing SC2 and it runs below 10 fps using the recommended settings - I tried lowering everything to "low" but that didn't help more than a few fps. Installing stuff on my PC takes an obscene amount of time - no change with the new HDD.
I ran a windows memory check - but my ram checks out fine.
On a further note my PC simply turn off at radom - a few times during startup as well - I have a 650W power supply - but maybe it is faulty?