The online fitting works well in my experience. That said, I would contact them and ask for their thoughts. The Nitro is driver only.
I get the testing with grips that don't work for you but I wouldn't worry about that. I play a larger specific one as well and had no issues.
Over the years I've had Titleist, TM and Ping in these shafts and Ping has always won out. I'm not sure why and Ping was 3rd for me with other shafts I was playing at the time. For some reason these pair up perfectly for me.