You could also check out some Neu Energy lipos. The Neu web store has recently dropped their prices and you can get a 4s 4100mah 30C lipo for $111. Its pretty close in price to zippy-R's, and from a top tier company.
Zippy packs are not enerland cells, they are china made.
I have been looking at a cheap big pack for my ebike. Compared to MA packs I could get 4 times the capacity with a higher discharge rate. The 10ah cells from MA are $1200 for 12s now! Otherwise it would be Polyquest packs that could very well last longer and would guaranteed be better matched. Ahh, choices choices.