I'm sure the "world famous" t-5 that Firebob is refering to is the world class or WCt-5 that was used in 3rd gens starting in '88. The earlier ones are refered to as non-world class . And yes the torque ratings on the WC's are just over 300 ft.pounds. From what I have heard what kills them is dumping the clutch at high rpms or speed shifting at high rpms. The Muncie is a stronger trans and the six-speed t56 from the 4th gens is stronger as well. The Tremec TKOs can handel up to 600 ft.pounds if you need a tranny that you can really pound on.
I have a WCt-5 in my Firebird and occasionally I break the tires loose from a stop sign and even chirp second gear from time to time. Haven't had any problems with it. I love the crisp shifting and the over-drive 5th gear is great on the highway.