75 mm....
or.
Gumballs 76mm
Strikers 77mm
Flywheels 76, 83, 90, 97

I assume that for a loosely set giant or a Super G even larger wheels would be an advantage.

In my opinion, there should be very little rules along these lines. Simple is good. Otherwise you open up all sorts of problems (and you limit progress in design experimentation.) Plus there would be too much time wasted on measuring and protesting.