At least you have narrowed your choices down to two. My knee jerk reaction is to go with the 1400kv motor, but I like to stay on the conservative side. I'd also go with the 1400kv motor to be able to gear up rather than having to gear down on the 7S setup. On the other hand, if you go with the 1700 kv motor, you will get GREAT performance on the 7S pack and still be able to run packs with less voltage and still get good performance. From what I have seen, the 1400 kv motor doesn't even really wake up until you get to 5S voltage range. With the 1700kv motor, you'll get good performance running anything from 5S A123 on up.

I think that I just talked myself into the 1700kv motor.