[stampy]

if you went with 4000mah packs and wonted to run them in series (positive to negitive) you would still end up with 4000mah the mah only increses if you run the packs in parallel (positive to positive). i would suggest running 1 3s2p6000mah pack and 1 2s2p6000mah pack wire them in series (positive to negitive) to get a 5s pack. series does only dubble the volts. in your case its 11.1 of the 3s pack and 7.4 of the 2s pack, wire them in series to get 18.5 volts