When I get these on 240 VAC the power supplies can supply 1200 watts each so I will switch to "High Efficiency Mode" which will pull power from only one supply and have the other in redundant very low power mode.
Wouldn't it be better to keep it on balanced and allow your PSUs to be more efficient?
i'd say that it's better to keep it balanced and steady. As supplies have certain (+/-) lifespan, "High Efficiency Mode" isnt contributing but most likely killing it sooner. Wouldnt you say that you'd be killing them one by one?