Pretty much that motor is identical in what it can do with the larger diameter, but same rated wattage motors.
Its a 500w rated motor, so yeah, 5000w is pushing it way too hard. It will take 2000w max watts for long durations fine, 48v 40 amps will get you the wattage to overcome wind resistance and get to the motors max rpm under load.
If it maxes out at about 30 mph, then it will cruise on 1000w, and it can do that all day. But the 2000w bursts at every stop light won't faze it, or it will be able to run at max power up a long hill fine, as long as it has enough power to keep rolling above 15 mph.
That would be ideal.. but you have a 72v battery. limit it to about 30 amps, also around 2000w. Your max speed will be higher, and cruise wattage more like 1500. But the motor can still handle that, if you just take a bit of care about overheating it on a long hill, or many starts and stops.
A very crude temp sensor attached to the axle, tucked under the nut in the dropout, can help you tell when your motor temps are rising too fast to keep riding that way. But you could ride that motor hard as hell for 700 watt hours, half your battery. So you could just ride like a mad man for the first 10 ah, then do a long slower (still 25-30 mph) cruise to cool er down.
Ventilate the cover, if you want to really push it hard, then you can just stop briefly, take a sniff, and know when to stop riding so fast. Toasty varnish, all ok, that burning smell, cool it off.
BTW,, if that controller is really overheating, then its because you are running it on the wrong phase order. It should get hot, but not overheat. Wrong order, one phase is pushing backwards, the other two forwards.
