Also the run time won't be half with the high voltage low kv example. Low kv motors use less amps, so the 22.2V 2500mAh lasts far longer than it first appears.

Power (Watts) = Volts x Amps

The low voltage high kv setup draws more amps to make the power, thus draining the larger capacity cells quicker. (All assuming correct setups including gearing of course)

One rule of thumb that is frequently mentioned, around 30,000 rpms seems to be the about the sweet spot (if not the maximum in my opinion) that works well for 1/8 electric buggies. 1400kv on 6S lipos, or 1900kv on 4S for ROAR rules seem to be the most popular. Much more tends to increase heat issues, reduces run time, generally any extra power is not very useable. Even a good 1700kv on 4S has an astonishing amount of power, the quickest one on track I have seen by far runs this setup.

Maybe a touch more if you want truly ridiculous power for fun, but again keeping temperatures in check might be a challenge and run time will be reduced.