zpb, please understand, I too have limited experince with the Neu motors. I can say that when I evaluate performance, I don't consider the heat factor. With the Feigao motors, the heat was troublesome, but not my main reason for going to the higher turn motors. The 7XL was just plain too much for the our track. The 8XL was better, but still too much. When I hit on the 9XL, everything came together for me. I was able to really work with the radio, without having to take too much care with the throttle and I was able to actually get to full throttle on our track. I posted a video in the brushless forum of my 8ight T with the 9XL running on 4S. If you haven't seen it, you should take a look. A Neu motor, of the same or similar kv rating, should surpass the performance of the 9XL by at least a bit.

I just don't want to give you advise that will leave you wanting more. For me, the 9XL was perfect at around 1800kv, so I'm figuring that the 1.5Y should be a bit better than the 9XL. That's why I went with what I did. Plus, the 1.5Y leaves a bit of room for going to 5S for better performance. All I have to do is swap battery packs.

I'm sure that you are aware of what happened with my Neu. It was just my suspicion, although I think that I am right, that I got a 2Y instead of a 1.5Y.

I will say that the motor ran very well. I liked it. I like the relatively mild setups, but the 2Y (I think) left even me wanting a bit more. If I had to make the decision in the 1512 line, I wouldn't go less than the 1.5Y, unless I was planning on going to 6S. In your situation, with the A123s and such, there are four motors that I'd be looking at. The 1512 1.5Y or 2.5d or the 1515 2.5d or 1Y.

In the 1512 line, there really isn't much difference in the kv ratings of the two motors, so I'd just get what was available. In the 1515 line, I'd go with the 2.5d for voltages similar to 4S or 5S lipo. If you are staying around 4S lipo voltage, I'd consider the either the 1Y or 2.5d. If I was buying this motor for myself, I'd so with the 2.5d for more voltage flexibility. On the other hand, I don't remember who it was, either BrianG or GlassDoctor, but one of them said that Mike gets better temps in his truck with the 1Y on 4S.

Decisions, decisions. I hate making the ones that cost lots of money.