They can handle a bunch when properly built.
I had mine built as a reverse-pattern, manual shift with a lock-up converter by Extreme Automatics in Ohio (www.extremeautomatics.com). They cut off the original tranny bellhousing and replace it with a billet Reid bell that bolts up directly to a Mopar smallblock so no adapter plate is needed.
Extreme's 200-4R build levels are:
Stage I 450HP/400Torque
Stage II 750HP/600 Torque
Stage III 1000HP/750 Torque
