The iB5 is a VERY strong box, been used plenty of times in ZT applications effectively. I don't know how much stronger the MTX is, if at all, but as far as I'm aware we are talking about a standard car here anyway and the MTX is the sloppiest, crappiest gearbox I've ever used and the IB5 is as tight as a drum, million times better changes and much quicker and snappier and is the correct gearbox for the car, so a straight swap anyway.