FWIW, I've had my new 4300 for about three weeks now. I consistently run it 3-6 hrs per day, avg 65-70 db, with 4 ohm speakers. It's warm at the end of the night, but not hot.
I'm considering picking up a 2-ch amp for my mains, not because I'm worried about heat, but just as a precaution to prolong it's longevity.
Bottom line, the thing is a beast. I couldn't be more pleased.