I wish I had the answer for this one, but I don’t. Googling on this subject didn’t help either.
Is it a max electrical input power rating or mechanical output power?
Is it continuous duty or just a “time limited” max?
Does anyone know for sure what these ratings on our BLDC motors stand for? Looking forward to contradictory answers… 
peak mechanical watts at max recommended motor current at max recommended battery voltage (angular speed rad/sec * torque newton meters) = watts mechanical
you can get the torque at peak mechanical power from:
battery current limit per motor (amps) * (60 / (2 * pi * KV)) = newton meters torque
electrical power at peak mechanical power:
battery current limit * battery voltage
copper loss @ peak mechanical:
battery current limit per motor * battery current limit per motor * winding resistance ohms = copper loss @ peak mechanical
example: 60a * 60a * 0.05ohm = 180w copper loss
peak mechanical watts:
electrical power at peak mechanical power - copper loss @ peak mechanical = ~ peak mechanical watts
motor angular speed @ peak mechanical:
peak mechanical watts / torque newton meters at peak mechanical = motor angular speed @ peak mechanical in radians per second (1 rad/sec = approximately 9.5493 revolutions per minute)
Absolutely nothing.
Just another meaningless number used by the marketing department.
This is pretty much the situation, you can’t compare manufactures wattage claims as they 1. tend to inflate them for MOREPOWERRRR 2. there is no standard test across manufactures. 3. There is no test standard that correlates to esk8 usage.
Larger motors can dissipate more heat, motors of the same stator and can size will have similar power ratings. With the exception of really nice / efficient motors that could get 10% more power in the same size before overheating.
I would say go with amps… for example, some 5065 might be able to take it up 40-45 A or so, while 60’ size might be good up to 60A or so…
Personally I have witnessed only 42A constant on my 6374 motor, while I rode single drive and it got relatively hot - hard to touch for longer than 1-2seconds…
So yeh, I guess thermal camera and some field experiments would be the way to go here…
I think general knowledge is that 5060 or so size, is good up to 1 - 1.5kw or so, while 60’ size ones can go up to 3kw… mostly ranging in 1.5-2kw range.