I would definitely invest in a quad core CPU if you plan to do a lot of things with it. DDR3 timings are awfully high, but still quite fast. They're more comparable to some of the fastest DDR2 around. Imagine how fast they would be once the timing come down?
I think Windows Vista 64 bit can handle anywhere from 16-128GB depending on what version you get. But motherboard will limit you anyways. I think it's like 8GB or something for the motherboards these days? That's a lot and I don't know if you will see a difference in performance--should you decide to install 8GB