I like your build above. A lot of people love the quads. Depends on what you want to do. If you do a lot of multi-tasking, a quad will be better for your. Most games don't as yet take advantage of multicores, so a faster processor, like the E8400 will give you a little better performance. Regarding memory, a DDR2 800 with a low latency (CL 4) gives you very good performance. The crucial ballistix worked extremely well with the motherboard which automatically detected its low latency timings. I love the gigabyte motherboard. Lots of great features and quality parts.
Enjoy
Enjoy