Honestly, I would splurge and go for the 8400's, I just picked up a pair myself. They're a bit more pricey, but the memory foam makes them easily the most comfortable headphones I've ever worn! I find that they've really improved my mixes as well as helped "place" sounds in the stereo field. They're also top notch for A/Bing your track vs. a professionally mastered track because you can pickup the subtle things.
A couple things to keep in mind:
The headphones require a bit of burn in to reach peak performance (around 80-100 hours), but they're still phenomenal straight out the box.
The headphones output a flat, uncolored response. I've heard complaints that they "don't put out enough bass," but that's what they're made for. IMO, the "bass" is very nice and accurate.