My experience has been with piston engines, but the note about 'cooling temp comes down when engine speeds come down' cought my eye.

This is a very typical result when the water is moving too fast thru both the block and the radiator...it needs a restrictor in the line (or thermostat), AND reduce the rotational speed of the pump (pulley size).

One technique I use with piston engine water pumps is to block the rear face of the impeller, so the exit of the pump is radially. This is an old and new stock car trick to reduce cavitation at the pump which WILL lower the water temp.

I'd attack this problem from MANY sides, and just enjoy the results, even if you don't know exactly which one works.

Good racing.

Bill