if your goal is purely speed, i'd go 4000kv on 3s. that setup is capable of theoretical speed beyond 100mph quite easily. here is something to consider though, will a 3s, or even a 2s, fit? pan cars typically run 1s and as far as i know only a few can fit a 2s. you wont be able to fit a 3s in the stock battery location. i know you are building an f1 car, but they have very similar specs from what i have seen.