It depends on the tolerances on the gears... many miles on the box is more backlash between gears so this makes it worse...
Most common issue however is 3rd gear and sometimes the 2nd gear... I have 400bhp and 520Nm of torque. I don't launch it off the line like a lunatic and I change gears slowly but I have broke 4 times the 3rd gear and most of the times with the engine at about 5000rpm... It has to do with torque and rpm imo mostly and not bhp...
what i did was to install an aftermarket boost controler and I made the car too produce boost without spikes and it helps alot, doesnt feel the same as before when you nail it but I am protecting the gearbox until the installation of stronger gears...