I'm not new to system building at all, just his is a perplexing decision between speed and upgradeability. Is the speed worth it or is being future proof worth it?
That's a personal call, really. Look at your older builds. How many of them did you drop more memory into? (I'm actually in the same boat as you are with deciding on parts of my latest build.)
My thoughts are that mainboards are going to end up going to DDR3 so that upgradability choices in my DDR2 memory are isolated to the single build. How likely am I to need more than 4GB of RAM in my new system before I upgrade the motherboard?
Your answer to that question should probably be the main deciding factor.
I suppose the other question, though, is how much you want to overclock. You've probably got built-in headroom with 1066. *But* you are also talking about OCing 4 memory modules, not 2, which can be a lot trickier in terms of getting the right timings.
My inclination is probably along the lines of NeXus^'s recommendation, though.