So I was using some 7500's on 3s and getting awesome speed on my micro. Got up to right around 70mph... but sadly they get a little too hot especially in this scorching humid weather in southeast tx.

I went down to some 6500's to see if that would help but they seem to get just as hot and I even lost some speed

I'm thinking of getting some 4000's which should solve the heat problem right? However I'll lose a lot of speed I'm sure. So I was wondering if there was a way to make up for the loss in rpms and still keep the high speed with the same 3s batteries? Would a bigger higher pitch prop do it?

What stator size motors are you using?

To see a real gain in performance you should consider bigger prop for a lower kv motor, but that mostly depends on thw motor size.

1105 motors