You'll probably find that the 4s lipo will be too much for the speedo to handle....... 60 amp speedos would be better. The motor, given adequate cooling will probably be fine with 4s, but to be perfectly honest, it will last a whole lot longer on 3s voltages and resulting current draw from the 7 blade fan unit. A three blade fan unit would probably be better if you really want to go for 4s. The new DF15 units with their new motors from eflie are a perfect match for the F15, and even tho they are pricey, are well worth the money due to the fact that they are hassle free and work exceptionally well....... even at 4s voltages