You makee a mistake on the spur gear , the stock e-revo spur gear is 68T, mod .8.
So with your 4s li-po, gear it with a 23T 32pitch pinion, and you'll be in the 39-40m/h

On my e-revo, on 6s, with badland tire (5.85" OD) i'll use a 22T pinion.