2650kv is only warranted up to 4S. 4S is "nuts" for a 2650 in a buggy. I ran 3S and it was fun but bad for runtimes. Plus, it wasn't smooth - it was like a 125cc 2-stroke motocross bike - lots of high RPM powerband but not much "grunt".

This year, I picked up two Castle 1800kv motors and 4S 30C Zippys. Much nicer setup. I can see where even higher voltage would be better. I do want to pick up a 5S 4000 to mess with. This setup also runs "ok" on a 3S pack I've got and in the only outdoor race I did with it this year, actually got very similar laptimes with 4S and 3S.

One thing you guys forgot to bring up is Motor Wattage. You can move from a 800watt 2000kv motor to a 1200watt 1400kv motor and higher voltage and maybe even still draw the same amps through an ESC. That would create more power and you'd want to definitely go to 6s for that. Would run cooler since you'd be faster and not on full throttle as much. A motor seems to want to draw at its wattage rating, it just has different RPM output with different voltage. I'd love to invest in a wattmeter and understand it better.

So, when doing motor calc - start with the vendor's motor wattage in the equation. In another thread, a guy with a Novak 4.5 running 2x2s lipos in parallel would be drawing 120A through his ESC - and he was saying it was having heat problems. That's apparent with such high Amps.