The losses thru the drive train will diminish as a % of power as the power increases ie don't expect a 300 kW car to have the same % loss as a 100 kW car.
In general, at the numbers we are dealing with here, add 1/3 of the rwkW to get fwkW, so, you should have approx 270 fwkW.
If you use a Dynamic Test Systems dyno, they have a procedure to accurately determine fwkW from rwkW.