I have the 2600k. I figured while I was at it I mine as well get the best of the best. I also do a lot of modelling and rendering so the hyper threading comes in handy.
It also is clocked an extra 100 mhz, and while that's not much for 100 dollars more, it does allow you to overclock higher. Some can pass 5 Ghz.
Though I'm staying at 4 Ghz until I get an aftermarket cooler.