[RC-Monster Mike]

I like the Kokams because they have the highest amp rating per ounce of battery. I race, so weight is a big concern for me (bigger than runtime).
You have the relationship between motor turn and current draw nailed, and your motor selections based on the 18.5 volts are on the money as well. And yes, around 40Krpms seems to be a nice place for the motors to be for performance and efficiency.
The impact the turns/amp draw has in a real situation is this - the hotter motor (less turns) will drain the batteries faster and produce more power on a given cell count. The higher turn motors are capable of the same power output (basically, all motors of the same family can produce the same power), but need higher voltage to to it. The higher voltage and lower amp draw will yield longer runtimes with the same capacity batteries, as well as increased efficiency and cooler temperatures in most cases.
It seems like you have a pretty solid understanding (got your head around it:)) of this stuff, actually.