You're able to run more on less amp draw with 240. Not more wattage. Maybe I said that wrong. If you have 100amp service, that's your limit. If you have 200amp service, that's your limit ...
I save maybe 1% Watts using EVGA G2/P2 ATX PSU's on 240v vs 120v. Some Server PSU have a big difference, like 4-5%, even as far as to have a TDP limit of 1100w on 240v or max 800w if they're plugged on 120v.
As for Amps, 240v is half the amp for the same wattage, that's why using 240v allowed me twice as much rigs in an apartment setup!
30a * 0.8 * 120v = 2880w limit
30a * 0.8 * 240v = 5760w limit
Basically, 240v is safer, since the risk is of burning down is a AMPERE thing. My rig will still pull 1kW~ but on 240v its 4A~ Instead of 8A~ so the power cord is cooler and less amp go through the socket.
1-2% is typical for savings on a gold-rated supply when using 234 VAC input instead of 117 VAC.
Probably a bit less on a Platinum or better rated supply.
Server PS that have a much lower wattage rating at 117 VAC are limited by the input circuitry only being designed to handle a certain amperage - it's NOT an "efficiency" difference causing the greatly different max power ratings.
Your APARTMENT panel is fed at 234 VAC - the total power draw is going to be basically the SAME if you feed the miners from 117VAC as if you feed them from 234 VAC, as you can pull *60* amps at 117 VAC of total current draw.
The only difference is going to be a very small increase in IIR losses at 117 VAC vs 234 VAC (which is also WHY your power supply is a hair more efficient at 234 VAC, reduced IIR losses in the input circuitry).
Changing to 234 VAC does NOT allow you "double the wattage".
It DOES allow you to use smaller wire gauge for the same power draw, or use the same wire gauge and run a lot cooler (which does reduce fire risk).