Safe rpm you could run all day at and not worry about getting the engine too hot and cause damage. You won't start floating the valve. I have had mine way past 5500 once going down a hill and it started floating the valves and sounded like it was about to come apart and you could smell the heat coming from under the seat.
Now for like drag racing short distances, I will run it up to 5000 in short burst but even then you can smell it getting hot.
Club Car school? They may teach you the basics but experience is the best education. I have been running no governor or limiter for the last 2 years and I have learned my limitations of what I can and can't do. I put well over 1200 miles and 320 hours on my cart last year alone. I have a tach and speedometer. Even at 4400rpms for over a mile, you can tell its getting hot. 4200rpms, I have gone for miles and miles and never smelt anything. Also, the GURU's at another cart site have told me the same safe RPM. Plus, it is safe to tell people that rpm. If you tell them they can do 5000rpms and have no problems, you are asking for lieabilty issues. First thing out of my mouth is... If you are going to disable any governor or limiter, buy a tach first. Be safe first.
I have also found a way to get up to 4mph faster with some drive clutch modifications. Doing testing on my design now. Using my worn faced clutch, the belt would only go up 2/3 of the way. Now it comes out of the clutch about 1/16" Gained 5mph with 23" and slowed the rpms down to a safer level.
Before: 24.6mph at around 5300rpms
After: 29.8mph @ 4700rpms.