As far as I'm aware Marc is 2nd and 3rd that takes all the abuse so theoretically I see no reason why what you are planning to be an issue, however that being said even uprated gears are not all that and its the torque that kills them, my frien kept destroying boxes (rwd mt75) so got a new box bigger stronger bearings and uprated gears (not cheap) 1st outing 7th lap at brands hatch it stripped the gears (running 430bhp 530Nm). Now he's going T5 and after myself also just doing another box im also contemplating T5 or possibly 350z box.