Low RPM reduced flow, High RPM increased heat. That's why I fitted the electric water pump. It runs at a fixed speed, has been fine on 30c trackdays & everywhere else.
At Low RPM it increases heat transfer & at High RPM it flows as much as the stock impeller so all good.
I swapped out my fan for a VTR unit originally, but make sure you add stone guard mesh or it will destroy your rad when it collects a kicked up stone larger than 1/4".
I then switched to 4x waterproof PC style fans mounted to the outside of the rads, requires some minor side fairing air vent edge trimming to fit perfectly. But with my 90c temp switch & a 25/50 Antifreeze to distilled water ratio, the bike runs great even with my increased power.
The electric fan is great at the end of a track or hard/hot session, you can kill the engine, but leave the ignition on for a few minutes & it keeps pumping the heat out!