I agree, the heated seats get very very hot. The manual also states that after a certain amount of time the ventilated seats go from 3 blue lights to 2 blue lights in order to keep the seats from being overworked or something. But yeah the ventilated seats keep you way cooler than the E60 M5's ventilated seats.
I could only personally take the heated seat setting on number 1, that was perfect for me.