That is correct about track size and configuration making a huge difference. Out here, I can easily dump a PolyRC 6000mah lipo under 20 minutes in the winter on a large track. When we get outdoors, I can swing 20 minutes.
A 4900mah 4S pack I have dumped in about 13 minutes on the indoor track. this is why I like the 10 minute main thing and think a 5000mah 4S pack is a great starting point to go with.
One other thing I would ask, can you make your packs such that there is zero cell shifting from the rigors of racing? I have seen in a variety of softcased lipos that with the current crop of trays used, the cells themselves will shift a bit. Not sure how much could be done short of a hardcase of shrinked in case like Maxamps offers, but figured I would ask.
It would be cool if someone made a connector using the same kind of plugs that Castle Creations includes for there Mamba Monster.