[Tambohamilton]

So far as I can tell from looking at them, the stiffness should be pretty similar. The sport mounts have a steel body instead of aluminium on the non-sport, I think, but the rubber parts seem to have very similar dimensions and the bearings are the same.
...I think. So I think the stiffness should be similar, unless the rubber is a significantly different compound.

The xD has a much sturdier base; thick cast aluminium with ribs, but the rubber part looks different enough (shallower) that it could completely negate the extra stiffness of the metal part.

In short, there's no way of telling without testing or factory specs, but it would be reasonable to assume that functionally they're not hugely different from each other in terms of stiffness.