Hum, keep in mind that higher voltage means higher RPM so higher losses in the motor bearings.
But for heavy trucks like truggys or MT, with the 2200kV, 5S with small gearing is the way to go, maybe on 6S the motor loses a lot of efficiency in the bearing...
A 1520 1Y on 6S should give you better efficiency anyway...
Brushlessboy, I would have a question : The efficiency at full throttle is best for the motor or ESC ? Or both ?
Inferno VE MMv3 NEU-CC 1515/1Y 4S "Flying machine"