Looking at the two different motor of the 4014 and 4012 options I would look at it this way, weight and horse power, if you are going to have a fairly light medium weight otco, then I would go with the 4012 if you think there is going to be a lot of weight, like 16lbs take off weight I would think about going up to the 4014, there you can get some more horse power out of it, bigger motor, more power.
When it comes to the KV, that kinda can be looked at like whats under the hood, so you have 4014, you can translate that to something like an 8 cylender motor, you know it has power but with the 400kv you will get great performance with speed of rotation but to relate a little more if you took a covette and hooked it up to a very large trailer with a lot of weight, then there are probably better motors to do the job like a big dodge ram truck - 330kv, it will offer less speed, less heat, and more toque.
So when you look at the KV that is the amount of revolution per volt you will get out of the motor. Here's a good example how this all works, I picked this off the web at -
http://www.brushlessrcmotor.com/brushless-motor-ratings/
Kv actually refers to the RPM of the motor per volt “without a load
Example #1: A 2500 Kv motor and a 2S Li-Po battery at 7.4 volts (2500 x 7.4) = 18,500 RPMs the same Kv motor on a 3S Li-Po battery at 11.1 volts (2500 x 11.1) = 27,750 RPMs
Example #2:
A 4800 Kv motor and a 2SLi-Po battery at 7.4 volts (4800 x 7.4) = 35,520 RPMs
the same Kv motor on a 3S Li-Po battery at 11.1 volts (4800 x 11.1) = 53,280 RPMs
To continue the lower the kv the more efficient with volts and heat, if you want something fast with less touque then you want the higher KV, in turn if you want something slower with more tourque then you want the lower kv, that is why as you start bringing down the KV you can start putting bigger props with more mass on the motors. So as you see there are some copters coming out where people are throwing 16 and 17 inch props on them. One of the way they are doing this, if you notice the motor sizes they are staring to get up to the 50xx and 60xx range.
When you start looking at the curcuferense of the motors not you can turn a lot more weight because of the horse power that comes with the size.
Sorry for the tangent I can keep going, at the end of the day I would say what you are doing here starts with weight, and what you are expecting to do with the copter, like more stability, high winds or very fast aggressive flying, or fast gopro-ish themed like flying then you would be looking at higher kv, however with that said you may loose some thrust options because the effecientcy that goes along with props as you go up in size and weight . If its a heavy production copter you are looking for with a heavier type camera, smoother slower fluent movements then you probably will start looking towards lower KV.
