I do 1st and 2nd gear blasts to rev limiter for fun on hiway entrance ramps.
If I ride with sportbike buddies, I cruise around 5200 for periods - 10 15 minutes or so, of course where permissible.
But without a real fairing (bikini, or half fairing) cruising about 5400 rpm (90+) becomes very tiring.
above 5000 RPM my 961 is smooth, and throttle response is great.
These crankcases on these 961 motors are heavy duty and built like brick sh**houses, and crankshaft is stout as well.
I seriously doubt that you can do much damage to these engines as configured (80HP) by extended hi speed cruise.
Dreer designed these engines to have none of the weaknesses of the old Commando motors.
He always admired the ruggedly strong Harley engine case design.
A lot of that beef went into the 961 case design.
Serious boat anchor material!