You COULD also, if you're not using the outlet at all, install a breaker box and run 110 lines out of it. On a 40a 220 line you should be able to run 3-4 20a 110 lines safely. If you don't feel comfortable doing that DIY, hire an electrician.
That sounds asinine. Why the fuck would you do that? Not saying that you can't do it, but why would you? You can run double the rigs at the same wattage on 240 as opposed to 120, because the amp draw is exactly 1/2, but you're ruling out the overload protection and equal distribution per outlet that a pdu will provide ... And better efficiency at 208/220/240.
Efficiency to a degree is valid, yes, though in my house I've noticed an extremely negligible difference when testing antminer PSUs (though they are SUPPOSED to have significant efficiency variance).
Draw? 4x120=480W. 2x240=480W. How are you running double the rigs on the same wattage?
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 ...