I'm currently using an i7-930 (2.8ghz); which is nice, but I've been in want of a faster chip. Hex-core would be great either for the bonus threads, or assigning 4 cores for rendering while using the other 2 for multitasking.
So is the price difference worth going up to the 3930k? As for cooling I might do a slight overclock --- the current [liquid] cooler I'm set on is a CoolIT ECO II-240, which is apparently identical to the H100.
Last option is wait till Haswell is out, but I don't believe they'll be selling hex-cores till a while after initial release.