Using a bit of maths, you can see that they're  similar.

Most batteries for other things use kilowat hours as their measurement. its basically energy over time.

if we mulitply our capacity and our voltage we'll get watt/hours, and divide by 1000 for KW/hours

so:

5s 2700mah :5 x 4.2v = 21v x 2.7 (Amp hours) = 56.7watt hours

4s 3300mah : 4 x 4.2v = 16.8v x 3.3(Amp hours) = 55.44 watt hours.


Rpm will be determined by KV, and power by the prop. You can get the same power with 4S but you'll chew more amps.