there is plenty of good ram out there. Yes the HZ's are nice but you can find numerous ram manufacturers that use the same IC's. Don't be lazy do some research yourself
Yes it is the Socket 775 LGA, but I don't see the nForce 590 SLI listed there.
I have very little knowledge of CPU's, but how much of a bottleneck are we talking about? If it will be extremely bad, I would be interested in possibly upgrading to a newer CPU. I have no idea what type I should look into that would be compatable with my setup nor the typical price range.