here's an example its hard to explain but I'll try
BRUSHLESS MOTOR A... kv 2000(2000rpm per volt) with 6s lipo(22.2volts). now this motor will push out 44,400 rpm and say a 12t pinion will allow for the proper head speed.(2100-2200).
BRUSHLESS SETUP TWIST 37....kv 3700(rpm per volt) with a 6s lipo (22.2 volts). first off this motor will now push out 82,140 rpm, that's 3700 X 22.2. already the motors rpms are well beyond the max for the motor and will be damaged. next to get the correct headspeed you would have to use a 6t pinion which I don't believe anyone makes simply because it probably would come apart. alright so we have established that the twist in no way can handle the 6s packs, but even a 4s pack will require you to use a 8t pinion which is still hard to find and you will be pushing the twist rpm limit of 50000(54760 w/8t).
ok then why is the high voltage setup better? because with the high voltage setup and pinion your getting the correct headspeed from more or less- VOLTAGE, as with the twist and its pinion your getting the same headspeed but at the cost of higher current draw(amps) from the battery. and all electricians know its not the voltage that kills you its the amps.
amps(current) = heat = damage
voltage = almost no heat=better efficiency=no motor or esc damage.
play around with this calculator http://www.e-helis.com/helicalc.php