Not true...
Have you seen the GForce T5 with the straight-cut dog/slider gearset? The GForce gearset in a stock case handles a boatload of torque/power, and with the new improved case they offer...even more.
Decent tranny up to around 600ft-lbs...especially considering how nice the form-factor is, and how nice a dog/slider transmission shifts. It would work well in a mild 385 build; especially in a light car like a fox body or a cobra street/strip car.
Furthermore, I can't tell you how many 450-500rwhp blown 5.0L T5 Equipped Mustangs I've tuned. Typically they make 450-470ft-lbs of torque and 450-500hp; all at the tires. This is more than some mild 429/460 builds; so I don't see why it wouldn't hold up just the same. As long as you're conscious about not powershifting 3rd gear (weakest spot), they hold up pretty darn well; even in stock form. The minute you start speed shifting the thing, that's when you'll pick a tooth off a gear...and all hell breaks loose. If you ever hear that lovely high frequency "tink" sound, do yourself a favor and get on the brakes and get that thing pulled over before the loose tooth finds itself between two gears that are trying to mesh.
But the G-Force T5 can be beat mercilously. I know several guys using them in hardcore race applications with engines producing 600+rwhp without failure.
Byron