What do you think is safe? We must keep a safety margin, don't we? On my hard disks, I always keep at least 15% of free space. In my car, whose engine can rev to 6,500 RPM, I rarely exceed 4,500.
Good chance they already engineered that 15% into the 6,500 red line. My 1978 Yamaha motorbike red lines at 9,000 I try to get there all the time. Come on let those horses run!