You should be able to hear your motor fine with earplugs in...
I had a '99 M750 with no tach. As hard as you'll be getting on the throttle at the track, I wouldn't worry... Also, it's impossible to over-rev the 750 motor. It will run out of breath before getting into the danger zone, rev-wise.
The bike will tell you when it's time to shift.... the more you ride it, the more you will feel it.
Good luck at the track, you're going to have a blast!