I'm loving the GS as a mal-style surf SUP and I don't miss the sidebites. But if money isn't an object, go the GT and then you have the option. Beside's maybe you want to crank it up a bit more than i do through the turns. But it's great as a single fin.
One thing I would suggest, is you check the position of the handle. Mine's a couple of cms further back than the balance point, even when i move the fin right to the front of the box. So u sort of have to pull up a bit with your front couple of fingers to offset it. WTF, Robbie? (not a HUGE deal unless you are carrying a fair distance)
The main things is, that s far as i can see in all the references to the 10'6.5 in this forum - everyone who has one loves it.
If you are anywhere near the sunny coast, go see the lads at Ocean Addicts. Top blokes to deal with, no BS, great service. And they are site sponsor so i guess it's ok for me to give em a wrap. I have no connection other than i've bought 3 boards there.