[BrianG]

Look at it this way, if you need, say 1000w to get the performance you want, the 3s/6xl setup will have to pull more current to get this than the 4s/8xl setup. So, I would go for the 4s setup - the weight gain from 3s to 4s is all but negligible.

Also, with higher current, the loaded kv is lower, so your actual loaded motor speed will be less, and might not get exactly the same top speed. Not to mention the inefficiencies dealing with high currents.