The longer the 812 burns in the better they will sound. A really marked improvement is reached after 100 hours, compared to their sound right out of the box. I go back and forth on any recordings between the 800 and the 812, and the 812 is superior to my ear. Not only does the 812 sound better, but the deeper ear cups are more comfortable than the more shallow ones on the 800.
Agreed, I don't understand why but many AKGs have a significant improvement over the burn-in. Sadly this means they may be disappointing at the beginning. The ear cup is very comfortable but I find it a bit tight for someone wearing glasses. The ear cup with 800 is more comfortable for me.