Mine should be around 380ish

Its more the torque you produce that kills the boxes, mine lasted a year at 370lb/ft lol. That on a t34 with a big lowish down spike.

Sounds silly, but the boxes last longer on bigger turbos as the torque is delivered higer up the revs and more smoothly.

I'd say the standard box would last fine on a stage 3 if you treat it with a wee bit of respect