[Sammus]

I read somewhere that the Neu's start to lose efficency above 50,000rpm. The way I think of that is to get close without going over. You 4s A123 setup should be 13.2V so you want to aim for something close to 50,000/13.2 = 3787kv.

I'm pretty sure the tekno fits 1515 size, so you would be looking at either the 1515/1D or 1.5D (4100kv and 2700kv respectively). I think the lower kv would be the better option so you have the option to go up to higher cells if you ever feel the need, whereas with the 4100 youre already pushing it beyond optimum with 13.2V (but how often will it be peak revving?)

To get closer to the 50k range you could go the 1512/1.5D (3300kv).

All that said, its just theory I've put together from my research without actually having any experience with these motors or cells, I'm fairly confident in my words, and I'm lead to believe any of the Neu's would be a huge leap up from a Feigao, but follow at your own risk :)

J2K: I dont think anything longer than 1515 fits in the revo with the tekno mount.