Motor basics. Electric motors are made up of 3 or more electromagnets pulling and/or pushing against 1 or more fixed magnet.
An electomagnet's magnetism is increased by the amound of turns of copper and the amount of current runnig through those turns.
If you have lots of turns of wire, that wire has to be thin to fit inside the motor, so it can't handle many amps, but it has strong magnetism, and lots of torque. This is a Low KV motor
If you have few turns of wire you can make that wire much fatter and still fit inside the motor, so while it has much less magnetism at the same current, you can push much more current through those fat wires and get some torque back. This is a high KV motor.
Generally the Max voltage rating of the motor is the short duration RPM rating of the bearings (often around 50,000) divided by the KV, or sometimes the RPM over which the manufaturer thinks the rotor will come apart. Either way running at RPMs up near where the manufacturor thinks things will fail is risky, and wears things out faster.
If you want any decent length of runtime while spinning a prop at 50k rpm, that prop would have to be tiny, and tiny props dont have a lot of thrust so acceleration suffers, and they are more prone to cavitation so aceleration suffers again. Prop sizing becomes problematic at small sizes too, going up one size from an x427 to an x430 is a 3mm increase as is going up one size from a x442 to an x445, but the 45 is only 15% more blade area, and going from 27 to 30 is 24% more blade area so it is much easier to accidentally overload your motor.
There is no common maximum current rating system to adhere to, but there is a current at which a wire will fuse quickly and as it happens quickly no amount of cooling will save it, so whilst some manufacturers underate their motors and some are rather optimistic, but generally amp ratings are reasonably realistic.
Manufacturer max power ratings however should be taken with a very large pinch of salt, again there is no common rating system to adhere to, and while one manufacturer may rate their motor at 1000W (for 10 minutes with no cooling), the next manufacturer may rate their similar motor at 3000W (for 10 seconds with excelent cooling).
Those 5692s are big heavy motors often put in big heavy boats, that need big props to push, and even though the RPM limits are lower than average at under 40k (due to the big heavy rotor), you would likely be better off spinning them slower than that, for example using the 730KV on 10s for 30,660rpm unloaded.
Paul Upton-Taylor, Greased Weasel Racing.
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