Well, the tire did rub.
Not on the fender, but on the center of the swing arm on the right side. It seems that centrifical force (Think top fuel dragster) causes the diameter of the tire to increase at speed. I ended up pulling the rear wheel, and grinding the weld smooth to gain the clearance. I don't know why, but the factory weld was almost 3/8" tall on the right side.
I touched it up with some black paint meant for wrought iron fences. While I had the grinder out, I took down the fender bolts to about 1/4". So far, no more rubbing.
Sorry, WD, not whitewalls, but I did get the raised white letters (Bridgestone Spitfire).
As far as advantages vs. disadvantages, I don't know if I'd go that big again. The handling is different, but the old factory IRCs were worn flat(bald) in the middle.
There is definalely a power loss, but the tradeoff is that first no longer feels like a tractor, fifth almost feels like an overdrive, and the motor isn't spinning it's guts out at 80mph.
I will have to be careful with my speed, as I suspect the speedo is off.