What should i upgrade first?

I am currently running 2 accounts find but i wish to run four what should i upgrade

Windows 7
8gb ripjaw Ram
AMD Phenom II X4 850 processor 3.3ghz
AMD Radeon Hd 6670 graphics card

Thanks In advance

[MiRai]

http://isboxer.com/wiki/HOWTO:Tweak_you ... ottlenecks

Whichever component is more of a bottleneck should receive an upgrade first.