I started an inquiry thread asking about the T31 GT vs normal T31 a week or so ago.
I did 100 miles or so breaking in the T31 GT on Angeles Crest Highway and Angeles Forest Highway this morning (twisty roads). I'm very happy with my purchase and will probably score another set from Chaparral via the price-match to the RMATV price. These are pretty darn good tires at $190 a set, if you ask me!
I also have a set of non-GT in reserves because I've been planning on getting a lighter bike. I also considered using them on the FJR after the GTs are done, for comparison sake.
Based on my experience with the GT, I'll probably reload on them. I was worried the stiffer sidewall would be unpleasant for my riding style (I was not a huge fan of the PR4GT). Turns out my concerns were not justified. There is virtually no price difference; actually, the GT were a couple bucks cheaper.