Some numbers with the extra turn, at 54V SPWM is 72% at idle, at 58V (absorption voltage) it's 69.2%.
Overcast today, so it's hard to get a number at 5.7kW/54V but I think around 85% is right.
At 5.7kW/47.5V it's up to 94.5%. Vout is stable at 238. I think this is plenty of headroom for my purposes, another extra turn might be pushing it though.
If it hits 100% Vout starts to sag? Had this problem with the egs002 and powerjack transformers, if Vin got below 52V the output sagged dramatically.
Not a problem with car charging, I stop it if batteries get much below float voltage, but it was a real problem with the resistive elements in the kiln, particularly at the end of the firing when temps were over 1000C. At less than 220V it struggled to push the temperatures higher.

Idle power is 35W.
Efficiency at 5.7kW/54V without the extra turn was 91%.
Efficiency at 5.7kW/47.5V with the extra turn is the same, 91%.
Will have to wait for a sunny day to get numbers at 54V with the extra turn.
These numbers depend on the accuracy of my clamp meter. I don't really believe them as they imply about 500W of waste heat in the inverter and I don't think it's that much.

Yes leave it where it is, no more turns, fortunately the controller will not let you hit 100%, the result of 100% PWM is hidden in your Forum Name.

The closer it gets to 99% the chances of AC sag as load fluctuates increases.

My figures likely won't match other inverters due to the way each of the 3 stack Toroids are wound.

Yes I guess 100% PWM is DC into the transformer...