Low voltage protection for a LiPo
Depth of discharge  DoD
Courtesy of Cadex , the best in battery testers ;)

Cycle life as a function of depth of discharge. A partial discharge reduces stress and prolongs battery life, so does a partial charge. Elevated temperature and high currents also affect cycle life.

Note: 100% DoD is a full cycle; 10% is very brief. Cycling in mid-state-of-charge would have best longevity.

Discharge cycles
          (NMC / LiPO4)

100% DoD ~300 / 600
80% DoD ~400 / 900
60% DoD ~600 / 1,500
40% DoD ~1,500 / 3,000
20% DoD ~1,500 / 9,000
10% DoD ~10,000 / 15,000


Thus if you choose 50%DoD which has a different cuttoff V depending on battery ESR and pulse current e.g. 25A/cell in 2P = 50 A you can expect short term capacity of 50% and for LiPO4 get more than 1,500 ~3,000 cycles say 2k cycles  vs 500 cycles or less    or net gain of 4*50% = 200% more life in Ah cum.

So do you want best short term Ah life or twice long term?[ Ah*cycle] using 50% DoD.

You do the math.  

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries