You might look into a good 600-class brushed motor with a 2.5:1 to 4:1 gearbox. I run just that with a 12V Multiplex 600 BB Turbo on 10 Reedy 3000 matched C-cell Nimhs that weigh 1.5 lbs. It turns an APC 11x7E on 2.5:1 reduction, and a 13x6 with 4:1 in an old timer with polyhedral wing of 52".
There's nothing wrong with brushless, as long as you get the efficiency.