Impossible to answer.

Different hardware, and amounts of hardware (hardware efficiency etc).
The you have to factor in the different electricity supplier costs.

Why not just take a note of your meter reading (assuming you have a meter) and extrapolate the cost after 24 hours crunching.

Welcome to the forums

Not much difference I imagine.......if a rig is on it's on.
The added draw from running at 100% (or 60% in your case) would be minimal.

Never ran at less than 100% and certainly haven't measured so it's all guesswork.

The inefficiency comes when using older hardware.......modern cpu's and power supplies are much better.

Try it and see I suppose.