Getting faster RAM is not going to help unless you change the locked motherboard. "Better RAM" is not going to fix the multiplier. Maybe you should get a new mobo, but not for the reasons you thought originally. I don't think this mobo fully supports your CPU. That's a good reason to upgrade.
Did you put this CPU in or did the PC come with it?
Any OCZ PSU will work fine for a single video card. Don't obsess over it. 600W is adequate for even two VGA cards and the quad. Like I said, don't obsess.
You seem bent on spending "x" dollars here. Just because you have the dough doesn't mean that you have to spend it.