I managed to have a conversation with the guys at hacker, who have now confused me even further

They think I definitely need the A100, and that whether I go for the 80 or the 100, I should run 6s2p for 8000 to 10000 mah... I'd hoped to go with the A80 and more like 6s1p, 4200mah. Their line of thought seems to add up to about 3.5lb more than mine, which feels wrong to me.
Doing all my sums for the weight, the theory looks like this:
Current DA-85 setup - 24.5 lb (fuelled up, to make it fair)
A80 / 6s1p 4200 - 23.5 lb
A100 / 6s2p 8400 - 27 lb
I guess my remaining question is whether I'm asking too much current of the theoretical two 6s4200 packs, and whether my flight times will be stupidly short...