TR-3550 rated from 350-475 lbs-ft (
TREMEC TR-3550 Transmission -Modern Driveline)
TKO-600 rated at 600 lbs-ft (
TREMEC TKO Transmission TKO-500 & TKO-600 -Modern Driveline)
The TR-3550 will live much longer behind 530 lbs-ft in a 2,400 pound car than it will in a 3,800 pound car - but much will depend upon how you drive it, how sticky your tires are, etc. If you're going to the drag strip with sticky slicks, then the TKO-600 is probably a good idea. If you're cruising with normal street tires the TR-3550 could last a long time.
Just my $0.02