Hello Brian 553,
Some thoughts from my side:
if the base oil is synthetic, it does have an already high VI. I suppose too high of a VI could mean the oil could shear rapidly over use,by the shearing of the VI improvers.
Normally these oils are used also for shocks, and if they are near the exhaust they could have a significant temp. This is where VI really maters, I doubt you will see a tremendous diff for the fork, except from riding in freezing conditions or in hot weather.
Frequent changes are more important for my motorcycle than the VI diffs among brands.