I sealed the gaps on mine as well and like you said the roll rate is very fast, I like it and mine is with the SFG as well. I am not sure if the roll rate is from the gap sealing or the plane design but I am one happy flyer as well.
Maidened mine yesterday, and wow, what a machine! =) This is just far above excellent! I used the Xoar 16x8, but forgot to take the temperatures after the flights, a lot of people at the field. It was -3-5 Celcius so wasn't to worried. I think I have to order another one just to have it ready to move all the equipment over, this is just too confidence-inspiring, and I'm sure I'll be too low sooner than later...
Thanks to Ohio AV8TOR for a very good building blog. Only thing different was that I have the "standard" motor mount for the Motrolfly, and had do drill new holes in it, some fiddling about and done. =)
Anyhow, what's the best technique to seal the gaps? I have blenderm tape, but has so far just used is as hinges for indoor/parkflyer/depron things.