I'm seriously considering changing my K701's for a pair of Q701's since they seem to improve upon my biggest complaint about the K701's, namely the lack of warmth! Not only have I read it from several people here, but I also read a review from the swedish magazine "Ljud & Bild" and they also claim that the Q701's are warmer and fuller-sounding than the K701's.
The detachable cable is also a nice plus
The downside is however that they're still using that **** headband from hell
One idea is to see if you can demo them and compare them side by side in the store. This is probably not possible. Some stores have a good return policy and will let you return them.
I think everyone here would be interested in knowing if there is a difference for you. Some may not be able to tell them apart, but I think it's quite easy.
I only had the K702 though, but did have the K701 about 5 years ago.
Too bad there isn't an online link for that magazine review. It'd be nice to read it.