[Patrick]

I've only had my neu 1515 2.5d (1700kv) running for about a week so far. I bought it to run in a truggy on 5s (TrueRc 8000mah, haven't gotten to use them yet so I can't say what they're like).
Since the truggy's not quite ready yet I thought I'd try it in my e-maxx (the neu). With 51/20 gearing on 12 and 14 cells it had about the same power and speed as a 7xl geared 51/13 on the same voltage. Except that the feigao would get to mid 50's degrees C (~130F+) or more with a fan and the neu got to 36 C (97F) with no fan and the quark was cooler.
Basically what I'm saying is that the 1515 2.5d seems to work well on 12 and 14 cell therefore should work on 4s, while still being able to run 5s reliably and 6s should be ok for some higher speed stuff, so the one motor can work in a lot of different setups.
Though if your going to use 4s only the 2200kv 1y would give better perfomance, and should be ok for 5s every once and a while.