I am running 500-540whp probably through mine with no failures. I didn't have any gear failures on the normal "built" trans I did for it when I put the car together either.
For power numbers, I always tell people, anything past about 650whp on a 2.0L and like 600whp on a stroker or some 2.0 turbo setups that make higher than standard torque numbers, is asking a lot and on borrowed time. The gears are too narrow to really take tons of abuse at high power levels. Obviously, people have had good luck higher than that, but definitely don't expect it, or just don't abuse the car much. You will shred 3rd or 4th gear, and usually take out the center diff housing, with a ton of power and passes. Weight also has a HUGE effect on this. Tin can 1G's will hold together much longer than a full weight 1G, VR4, 2G DSM etc. It seems a lot is fluid/heat related also, so try to avoid hot-lapping the car, and try running a higher quality maybe thicker fluid. I run Motul Comp Gear 75W140.
For the guys shooting for 700+hp, Auto or full aftermarket gearsets are really the only reliable option long term.
