I built what was a pretty neat system at the time. I can't remember all the specs but it went something in the way of this:
4GB DDR3 1600
2x 1TB HDD
Then my mate upgraded to the i7 chipset and that was heaps better than mine. (We run quite intensive gaming and CAD/Rendering). By that time I was wanting (needing) an upgrade but was low on cash for a full rebuild so I just bought...
SOLID STATE HARD DRIVE.
No joke, best bang for buck upgrade for any PC. Everything is sooooo much faster now. Recommended upgrade! Obviously his one still runs sims way faster than mine but for everyday multitasking solid state HDD rules. Just make sure your OS is on it.