Why bother with hyperthreading?! Games have next to no use/improvement in performance with the 2600k over the 2500k - which is why i didn't go for it. On top of that, the only thing good for HT is really seen in video transcoding - but in a month or so when the Z68 comes out, Quick Sync will be available and HT performance will be nullified in transcoding performance!
You mobo choice is solely dependant on your purpose - Gaming? Are you going to go SLI/CrossfireX ? If you are, will it be for 2 cards now / 1 card for now / possibly 3 or more cards in the future?
Mind you, Kepler generation GPUs are next in nVidias lineup on the 28nm manufacturing process, and we will see the end of Fermi's lifespan. That's when you'll see much higher graphics power with far lower power consumption - which will definitely superseed multiple cards (sli/crossfire) and make you choose 1 card over 2 cards now (an inevitable cycle).
If you're talking for present day, assess your needs, with enough headroom to leave you options. I say SLi/Crossfire capability is great and leaves you options. If you game at 1080p, i hardly see the need for more than 1 gfx card. A gtx 580 will decimate any game on max settings (with the exception of a minor few), so assess your needs and we can try to help further