I don't know how you figure you can do all that damage without the mage dying. As I recall, that mage only has like 80 hp. So thats theoretical damage, I assume?
Anyway, for my highest damage, once I got Edwin to cast Time Stop against the group of Fallen Paladins, cast two Abi-Dalzims into the fray, a flame arrow, and two magic missles. The ensuing damage was about 400 or so. Everyone died