Ok, we are on the same page... Usually when you up size (equally front/rear) the bike is naturally taller, and this does throw some riders off their game. Reality is you have to re-learn the bike, just as when it was new. Taller is Not always better tho. Some bikes squat better.
Those giant ass tires on choppers are just for looks, and are actually quite dangerous because of all the un-sprung weight. Blowouts happen, and people get hurt because of them.
Anyway... I don't own an S-8 but there is a thread on here where the owner went up one on the rear, and touted it as a night, and day improvement. I believe it was in the last 6 months, so I'm either mistaken or you did not find/see it.
Maybe someone will chime in here...
The ZX -50 is the bike I went up on the sizes so dramaticly. I actually have two rear desiginated tires on the bike.
The reason is I built the bike to run 1 mile speed runs, and modified the frame accordingly. It is 3.75" longer, and 1/75" shorter in the front, and rear. I went w/ a rear des. tire on the front to change the steering angle,(geometry), and give better straight line tracking.
I have ridden it as is on the street, and it handles like a dream, when before (oem) it fought hard to under steer.
If you do go larger on the rear you most likely will want to go larger on the front as well to keep the factory geometry (if that's what you like)