An optimal solution can only be found for a single load condition. Usually MOSFETs are driven at the Vgs provided in the datasheet to minimize Rds since maximum load current is the thermally critical operating point. 10V would be a very common drive voltage for a discrete Si-MOSFET. If you can get away with a much smaller Vgs (higher Rds) at full load, you might as well reconsider your MOSFET choice and look for one with lower Qg and higher Rds. On the other hand you have to keep driver losses within reasonable margins to not thermally overload the driver chip.