Ram: 6GB, guess that sounds smart for a new system I would get 6gb probably too if building with DDR2 because its dirt cheap. However DDR3 is not so cheap, also its early in its devolopment. The gains from 4gb to 6gb are none unless your doing very specific tasks that can break the 4gb barrier like RAM preview in video editing, or maybe ultra ultra high end gaming but I doubt even gaming can break that limit considering the card(s) your using.
This is another area where I can say get 4gb now, see how it is, and later upgrade to 6gb if you need it. By that time DDR3 will mature to be a better product and be cheaper.
Core i7 uses triple channel memory. And is DDR3 only. Going 4GB would nullify one of i7's most impressive abilities - it's sheer memory bandwidth.
So if going i7, there is no choice - it's gotta be DDR3, and unless you want to deliberately bottleneck the CPU, there's either 3, 6 or 12GB of RAM.
edit: If I go i7 in the near future (which I
might) it'll be the Core i7 920, 6GB RAM, Gigabyte X58-UD5 that I get.
edit 2: OCZ own PC Power and Cooling now, anyway, so... ;)