Here's what I think would be best if you absolutely have to build right now.
You're spending a LOT on this system, so you don't want your expensive parts to be obsolete in 3 months.
Get a good, cheap, fun mobo. I'd say the MSI P45 DDR3 mobo, as there's an open box one for $195 on newegg. Lots of peope have had great performance on this board and on water you can expect great OCs on both cpu and memory. I had that gigabyte mobo you're looking at, and I was revolted and chose to RMA. Now before sending it away it I did crank volts with impunity and eventually learn to love it, but it has very little detail control for the serious overclocker and I would not recommend it.
Then get a good, cheaper, fun chip, something that's going to to keep you occupied OCing. This is really your call, but personally i'd pick up a Wolfie. At the very least bump down to a Q9650, take advantage of newegg's recent price dip, and save 500 bones.
Either:
A) Put all this extra cash into better parts a/o cooling or other mods so you won't regret having cheaped in a month or two (i.e. 4870x2...)
or B) SAVE UP FOR NEHALEM!!!!

personally I'm a fan of the latter.