T6 is what, $30/gallon? I think that's what it is, or was last time I bought some (November 2015) when I did the oil change in my truck. $140 with tax for an oil change. Normally I use Kubota 15w40 in it, and it runs perfect with it all year long. Winter time sometimes I'll try T6 just because I want to, I can't tell any difference as far as mileage, power, noise, or anything else for that matter....other than my wallet doesn't like it. Anyway I had a little T6 left over and did an oil and filter on my G1900, using T6. Always used Kubota 15w40, so this is the first time for T6. Absolutely no difference whatsoever.
First time I tried T6 in the truck (old 7.3L IH/Ford), I thought right away that the engine was smoother and a little quieter when cold. This past November after changing the oil again from 15w40 to 5w40, I listened closely...and no difference whatsoever. That engine has HUEI injectors so if there was any difference I should have noticed, as the HUEI system is really sensitive to engine oil quality. I always know when it's time to change oil....so maybe my brain and ears were playing tricks on me, trying to justify spending the extra $40 or so for the engine oil.
So between those two examples, my own experience, I say T6 is a waste of money unless you can get it on sale for the same price as Rotella T or Kubota 15w40.