Figures of "efficiency" do not really apply for (MOSFET) gate driver circuits: as the gate itself does not "consume" any power the efficiency is generally 0 %.

If you want to optimize the power consumption of the gate driver, other influences are important: desired switch on/switch off (transition) times, gate characteristics (primarily gate capacitance), switching frequency etc.

Nice to see you considering efficiency of gate driver circuit.

The total power input in any converter may be considered as power input to the converter along with power drawn from all bias supplies. whereas, gate-driver is concerned, as U. Dreher said, it does not consume power, if it is so, then efficiency should be 100%, but gate driver consumes power from bias supply and deliver to switch, so we can not say its efficiency to be 0% or 100%.

A garte driver consumes power. The minum power consummed by a gate driver is     Qg x Vg x fs where Qg is the gate charge, Vs the gate voltage and fs the switching frequency.

Then you have to add the power consumed by the gate circuit driver itself, which usually is much less.

By the way, in you case I think that the simplest solution is to use a pulse transformer.