What does the windows performance test say as far as where any slow downs might be?
It will tell you if the memory or hard drive is bottle-necking the system performance.
Maybe run some benchmarking software to see what it can tell you.
I decided to buy the processor, double my ram and new video card,
first time I've gotten so much boost from staying with the same motherboard.
Will post here once I get it all going and maybe run some render tests to see how they match up with your system.
I also use FinalRender, I find it easiest.