Can't help you with the dissipation ratings, sorry. I've tried various 845s, starting with the cheapest Chinese ones, then the 845Bs from Super TNT and elsewhere, and ultimately the ones from Sophia, These took my amps to a new level of clarity and dynamics, quite a marked improvement over the "B's". One of my first Sophias went bad after a litle more than a year, but I've had no further problems. The current pair has been in place for around 8 months IIRC. Dave