I would go for whatever batteries you have more of. The 6s setup draws way less amps, so I usually prefer to go that route when available. But I'm pretty sure the guys that have a bunch of 4s 4000+'s laying around for their 8s systems, they would benefit from the 4s setup. Either way, I believe ken can get you around the same power. 1700w on these 58"-60" birds is way overkill anyways, even if its 2-300w less, you probably would barely even notice. Since flying the ballistic setups and the lighter setups with a bit less power, I've actually started preferring the setups with slightly less power. Although it seems weird, the lower power setups have drastically made me more smooth of a 3d pilot. The ballistic power is cool for tumbles and snaps, but I don't think I progressed as quickly with them as I did with my lighter, lower powered setups. Just my taste at the time though. My 51" slick is setup ballistic and I still love it! I just fly it different than my 71 on 6s...