You have to take into account what "reliably" means. 100k miles? 150k miles? 200k miles?
Understanding that the mechanical limits of the transmission will likely be a good bit higher then what can be done reliably. If I had to guess there is probably about 5-10% of wiggle room to the theoretical reliable power rating of the transmission (~385-400 lb/ft torque).
The mechanical limits are probably dictated by the wet-clutches first, then the planetary gear clutches, then the planetary gears themselves. I wouldn't be surprised to find the transmission unable to hold/transmit more than 25-30% torque then designed (~460-480), sure there are plenty of examples where this number is much higher, but then its just a matter of how long will it last.
But at the end of the day, even if the transmission could only hold up to 400 tq reliably, if you were making 400 tq to redline, that is almost 500 hp. (HP = (TQ * RPM)/5252). The stock 370 ft/lbs, if it were held as a flat torque curve, is 460 HP. I dont know about you, but if it were achievable and reliable on the stock turbo and engine block/heads, another 80-120 hp is plenty for this platform.