I have both the Q701 and the HD800. The Sennheiser is certainly better, but on many recordings I still prefer the AKG. I recently purchased the new AKG K712 pro, and I prefer it now over the Q701. The Q is an excellent performer, but the 712 adds a little more bass, while retaining the wide open and detailed sound these cans are known for. The 712 also has a flat leather headband that does away with the head bumps on the previous versions, as well as a redesigned ear pads. All in all I think they sound better than the Q and they are more comfortable to wear. I had a hard time finding these in the US, but thanks to a post here on headfi, I found them online from razor dog for $399.00.
I ended up cutting those bumps off of my Q701 because they were causing problems on long listening sessions. I thought about buying the memory foam pads from the 712 to try on my 701 because from what I've heard, the driver is the same and that's all they did to get the new sound. Not sure if there is any truth to that. I don't want to pay $80 plus shipping for pads though.