I d tell you that
20c turnigy 4s 5000mah hardcases is 666mah per buck, they give 400 cycles 1,5 years at good rates 4.15-3,7, more voltage sag after that and so on (used by me as 20s1p)
20c(real10c) zippy are half c rate and lower cycle life is my guess than turnigy above, from a guy and that was my decision not to get that brand, but still they are in good cost range for some. 525mah per buck for 6s 8000mah, cycles I don't know but for high performance i would estimate less.
nano tech 25-50c 6s 8000mah gets you 466mah per buck but also more cycles. for you application xx2p
good luck keep safe