It can be looked at from the other perspective also. Sennheiser departed from their traditional HD600/HD650 sound signature to compete with AKG. Considering how long it took Sennheiser to Launch the HD800 from the HD600 (omitting HD650 as it is a different flavour), 5 years development is quite short. It is a never ending battle of the flagships . But I guess this is the long awaited flagship since the K1000 which makes this more exciting and much longer wait. Hope AKG doesn't disappoint.
So far very impressed with the sensitivity ratings of the headphone. Even if AKG manages to match the technical capabilities of HD800, I think they have a better product sonically.