I wound up getting the FF15's in 20x10 and 20x11.
Unfortunately the MPSS 315/35/20's are out of stock everywhere, so I haven't had a chance to put them on yet. I was originally going for the FF01's, but then carguy's thread on the FF15's completely sold me on them, particularly how they look on...
It is not a straightforward mod.
You should look around and see what shops change gears regularly.
I made the mistake a few years back and brought my '08 to a shop that didn't do them on a regular basis, and the result was a howling sound in the back. I eventually found a shop that...
How much harsher is the ride now that you're on 20's?
I'm thinking of going 20's myself, since its a little more difficult to find wider tire sizes on 19's.
I've noticed this happening to mine as well, although I have a 2015 GT with 6MT and PP.
I was driving in 2nd gear and laid off the accelerator just like you did and noticed a whine. It does not happen when I am accelerating.
I think it may be with gears in the back though, and not the tires...