So far, it seems that M5 owners do not believe the motor is underrated by BMW.
http://www.m5board.com/vbulletin/sho...d.php?p=995614
Again, I think the 335 is underrated because it is impinging on M3 territory already. I do not think the E92 M3 will be underrated. To do so would only hinder BMW's efforts to distance the M3 from the 335.