G9x user here. I play games semi-professionally ("invite" level and I supplement my income by streaming, YT, and lessons), so my priorities are about as weighted towards consistant tracking as can be, but I still concede to the bigger picture when it comes to mouse choice.
Built in acceleration really is an overblown factor. Many of the best FPS gamers use it. So long as the acceleration is consistant, your brain will adapt and compensate. It really only becomes an issue when making tiny snap precision movements, and even then it is hardly noticable.
Comfortable grip, glide, and features (buttons, DPI adjustability/range, polling rate, etc.) are much more important considerations.