If you need it now, yeah, it sounds like a decent deal. However, I would get the 2.8GHz and save money towards future upgrades. You should be able to put 6-core in it from aftermarket and save some $
From my perspective at least, the 3.2 QC offers little value for the $. I'm going w/ the 2.8 QC because I can't justify spending more $ (I'm just a hobbyist). But if I were to spend more $ I'd skip over the 3.2QC and go for the 6core b/c it's a better value prop -- faster and will be relevant longer than the 3.2QC.
Not yet, someone has to try it before we know for sure. When these machines arrive, we can at least compare the EFI version of quad and six core, that should provide some backup. Also, I can't see any reasonable reason why Apple would use different board for 6-core and quad core