I will mainly be running 3s batts though.
Just gear the motor slow enough that the speed control doesn't get too hot (you'll still be able to gear this combo high enough without overheating that a 2wd slash flips over from air trapped under the body).
Though the sidewinder is not technically rated for 3s on the 3800, I've heard of people doing it successfully. Electric motors produce however much power (and draw however much current) is required to spin at their designed kV(within reason), so the trick is just gearing properly. Since the 3800kV spins slower, you can gear it for a slower speed than the 4600, in which case it will draw less current and run cooler (because going slower requires less power).
What you loose out on with the sidewinder/3800 is the ability to gear the 3800 to the motor's reasonable limit (usually identified by temperature, the faster you gear the truck, the hotter the motor, esc, and battery will get), since the speed control will run too hot (presumably, since castle doesn't rate it for 3S with the 3800 but does rate the mmp for 3S with the 3800) before the motor starts to run too hot. You can still gear the sidewinder/3800kV combo to go as fast or faster before the ESC gets too hot than you can gear the sidewinder/4600kV combo to go before the motor or ESC gets too hot. With the 3800kV on 3S, I'm confident that's faster than a 2wd slash can handle, it's probably right at the limit of what a 2wd slash can handle with the 4600kV on 3S, but with the 3800kV you have a much better chance of being able to gear it low enough to be controllable even on 3S than you do with the 4600kV. Even with the velineon motor, most people find 3S to be uncontrollable in this truck, however, and I suspect you'll ultimately end up driving it on 2S most of the time. SMC, SPC, and other brands recommended on hear sell good lipos at lower prices than you'll find in stores, so if you do find 3S to be uncontrollable, you can get a 2S for a reasonable price.
(Last edited by vintage : 9.16.16 at 10:16 am)