I guess for the lighter and much lower torque generating VVC, the dif is not as critical, but (rally_)Matt runs the quaife on his ZR 160 rally cars (even if they did start life as 25's on the paperwork). Although he did switch to a custom one a friend of his built - although I am not sure if he switched them on all the cars.
I found personally with the diesel and the huge slug of torque they generate, the quaife on the road was one of the biggest differences I found, as I have to be be being really stupid to get the car to understeer now - with the change in suspension, that limit is now even higher than it was before.
Short of driver tuition, the diff is Matt's honest opinion for the gaining the biggest jump in laptime over a 'standard' car/setup if you were to do just the one mod to it.
Either way - really good post, glad to see that you have got what you hoped to get out the car and long may it continue
