the 1st SC car that had been done had done 100k and has now done about 13k miles and is still on OE clutch and same box, no problems.....
obviously the gearbox is a known weak point anyway, so im guessing it comes down to how the person driving actually changes gear more than the extra power? i.e pulling away hard in 1st and banging it through the gears is gona kill it alot quicker than fast driving with a better shift.