I'd agree that higher temps are not efficient. It brings the wire resistance up and hurts the magnets performance so a loss for sure.
The nice thing about motors is they pull the power they need so overall output isn't that big a concern too me personally. Most of these motors are overkill for our apps regardless. BUT, like you mentioned, if they are running hot it's not an ideal setup.
If we're looking at efficiency I'd continue to look at the entire package. I'd eliminate the motor connectors (deans/bullets/everything). I don't care what they say, with the current levels these systems are capable of pulling (160A in cases), they're not efficient. Wire length/guage should be checked, etc (I'm direct wired on the motor).
If I can stay in the 130-140 range, I'd be ok with that at this point. Obviously if I could roll at 100* it would be better for sure. With the only slight decrease in kv, one shouldn't even feel the top end difference (1850rpm @ 18.5v).
IDK, I guess I'll have to see how that 1520 works for you. My guess is, it'll be better on shorter course slower tracks where there is a lot of part throttle (prolly be better with high traction surfaces too). Longer, tracks with fair WOT time, the increased efficiency will probably be curtailed some due to the overall greater power it "should" consume.
It's only ~75gr heavier so coupled with a RX8, it's tolerable for sure mass wise.
Alright, it's growing on me some more
