The 3000+ combo, you can EASILY o/c the 300+ to the speed of the 3500+ on stock cooling, and it saves you $100
edit:
and is this the PC you are settling on? a real shame you couldn't get the parts from newegg, as with your budget, you could have gotten a MONSTER KILLER gaming pc, complete with the512mb 7800gtx and dual core athlon 64 4400+.