Too bad there aren’t big quilt shows going on so you can try a number of different brands out. What makes you prefer the Gammil and Bernina? I am a Bernina girl through and through for regular sewing machines, but at least some of the long arms are t up to professional standards IMHO. They advertise the “advantages of using domestic needles instead of professional round head needles; not an advantage at all since the flat back ones aren’t as strong. The Bernina macho e is also more expensive tha equivalent machines. However Bernina dealers are generally very good about hand holding, and a lot of people feel more comfortable with that. (That is not a dig at those who need/want handholding!) I prefer a pro style machine that allows a lot of user maintenance and isn’t very picky about threads. When I went looking at long arms I was able to spend two plus hours playing with one at a very helpful manufacturer (Nolting is a gem among manufacturers) only to find out I didn’t like long arming! I had a deep need to feel the fabric as I quilted. Odd I know, but I ended up with a HandiQuilter sitdown.
Summary: find some place, probably multiple places, that will let you play with their machines at length. Ask about different threads. Spend time. You are the only person who knows what you will like in the end.