The main on-track benefit of LiPo is at the end of the run - whereas NiMH will have dropped off a little, LiPo voltage will be as high on the last lap as it was on the first. At least, thats what I've found in TC (27t and 10.5).
First time I've heard about capacity limits. Trakpower do 5400mah packs, Checkpoint do (although I think they are produced by Trakpower), MaxAmps and more. I thought it was to do with physical size of the packs - bigger cells etc.
And special cells? In TC this very much still exists.
