KV and runtimes

[mjderstine]

hey guys, I wanted to ask a question to clear this up in my own head, and since you have all been doing this for a long time, i thought you could put some of this in layman's terms for me.

(I am using fictional numbers, because its easiest, and i hope that will stop people from just correcting my numbers, and not answering the questions)

Say i have a 4c 5mah lipo, around 30C for starters.
my speed goal is around 37-40 mph. (what i think is standard for a 1/8th buggy)
I have the option to buy a 36-70 medusa motor but which KV do the best for runtimes? (that is my main question)

2300, 2000, or 1600. i assume gearing will be able to be adjusted for each motor to result in around the same final speed on each.
will gearing for the same speed on all the motors overstress any of them with only using a 4cell lipo?
would you think the ESC may get over stressed if the 1600 was geared to the same speed as a 2300, (approx. 37-40mph)?
keep in mind that i am planning to use a MM, not a MMM. (i have a MM on hand already)
and then will the runtime be different for each motor geared at similar speeds. i was under the impression that a lower 1600KV motor is more efficient, thus allowing for longer run-times, but is there a trade-off if i gear for the same stock speed at a 2300 motor?