so ok , let me put it another way , youve got one of your front wheels on the grass and you accelerate away , it spins up , what happens ?

youve got both your front wheels on the grass/ some loose surface and teh backs are on tarmac with plenty of grip ? what happens ??

trust me , at 5mph on a roller brake tester for 15 secs will NOT damage your diffs in any way what so ever