Hey Nick, I think you will be better off with a smaller impeller still. I started out with 110mm prop with various pitches, and working my way down 80mm, 64mm, 60mm, 58mm, 56mm. With the proper pitch (super low pitch) I could get the same thrust with 110mm prop direct drive as I could with a small diameter setup. We know from this forum that a 56mm impeller works well for a small 56 diameter motor so best not stray too far from that in my opinion. These little motors don’t have enough torque for crank around a larger impeller and prop for high thrust so smaller is better. smaller get higher RPMs and have much more thrust but in smaller jet of water VS larger prop pushing more water slower which requires more torque/reduction gear.
A 58mm impeller requires roughly 6,000 watts power, and a 64mm impeller requires 12,000 watts. Huge difference with an impeller only being a few millimeters larger. Stats from MHZ website.
Yes the 56 series inrunners say they give out 12,000- 15,000 watts but when you run the numbers which are 120A x 50v = 6000w, then calculate efficiency which 70-80% for rough numbers sake you are looking at only providing $4,200w to 4,800w mechanical power, meaning you’re way under powered for a 64mm impeller.
Hope this helps shed some lite!