We have tested with 3s and 6s setups with the same ESC, which gives us rpm feedback etc., and with 3s lipo we get about 19k electrical rpm and about 3.9kg of thrust, but using 6s we get about 25k erpm (and a quite frightening sound) which boosts the thrust up to about 5.9kg. After 70% duty cycle the rpm will not increase, so using 6s pack you are going over what the motor can actually do. Also efficiency drops significantly when going over 20k erpm, at 25k erpm the thrust is 50% more and power consumption is 100% more. When using 6s you should not use full DC as it will not give you any benefits. I assume with 4s you can pretty much have the max power the thruster has to offer.