As pilotpete2 suggested, there is really nothing even similar between the two batteries. The sub C cells have a much lower impedance which as pete said greatly increases their ability to maintain voltage while under high current loads. Put the same load on the AA cells and they will fall on their face. Nixx batteries do not have a "C" rating like Lixx batteries but if they did, the sub C cells would have a much higher "C" rating than the AA. From there, the sub C cells are much more rugged. The AA batteries tend to lose capacity fairly quickly tapering off quite a bit after just a couple of seasons. The sub C cells can still maintain much of their capacity after 5 or more years. Even just looking at the batteries tells you something. The sub C cells are not bigger and heavier for no reason. They are larger by design.

With all that said, with the far superior A123 LiFe batteries that are now available and at very reasonable prices, Nixx batteries are no longer my "battery of choice".