I have no idea what would be ideal for a board. But I can speak from experience with bikes.
Hub motors only get bad inefficient when they are overloaded. Mid drive has the advantage, of being able to shift to lower gears when overloaded.
At some point with either, there is a sweet spot where efficiency is less, but not so bad you overheat shit, and there is decent power to do what you need. A combination of load and rpm. Time to overheat is one way to get a quick estimate of if it sucks bad, or is ok.
The key thing here is overloaded. kind of hard to overload a big enough hub motor, and you can set one permanently in a lower gear by using a smaller diameter wheel.
So as always, "it depends"
The catch 22 on a big powerful fast DD hubmotor is,, you will not get great watthours per mile hauling ass up hills loaded heavy. This is not to be confused with inefficiency. The motor CAN haul ass up the hill running at an efficient rpm. It just costs watts to weigh a vehicle down heavy, then haul ass, uphill, or even on the flat. You just have weight, and fast means wind resistance. Basic Mechanical Physics.
But take your big powerful hub motor in 26" bike wheel, and a typical bike and person weight under 300 pounds, and ride it 10 mph on the flat, and the motor is under so little load that it can get a great wh/mi compared to another, lower speed wind motor. The key thing here is that the big ass motor is never close to overloaded. And then you pedal, and the motor is barely ticking over going 10 mph. Your pedaling is putting out 75% of what you need, so of course the amount of your battery you use is tiny.
Sure,, if you always ride 10 mph, the lower speed wind does do a better efficiency, but not by a huge number, not by 20%. Maybe more like 5%. I am meaning the change in the wh/mi you use. The thing is, if you are pedaling up 75% of it, a relatively big change in the last 25% is still a damn tiny number. Overheat in 10 hours, overheat in 15 hours, what's the diff?
The key thing here, is the big motor is never overloaded. Obviously it's not overloaded on the flat, but on a big hill it's not overloaded either. If you can manage 15 mph up a huge mountain, you will still be turning that motor in a reasonably efficient rpm.
So that's it for hub motors. THE KEY THING IS DON'T OVERLOAD THE MOTOR. This is why I mentioned 300 pounds. Most 500w rated motors run on 1000w can get up a big hill just fine, with grades under 10%. You can overload the motor with both weight and grade, so increase either, and you might slow your max rpm enough to be overloaded.
People will argue what is overloaded, but my experience is that 500w rated hub motors start to suffer in 26" wheels when they can't climb a hill faster than 12-15 mph. This happens above 10% grades for a 200 pound man, on a bike that weighs 100 pounds including cargo.
This monster of a bike, loaded to 450 pounds, gets up 8% just fine, at 15 mph. It had a big crystalyte motor able to run at 33 mph on 48v 40 amps. Yet it could also get a very nice watt hours per mile while going 15 mph on the flat. Good enough efficiency for an 80 mile day.
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Now,, you want to really improve the efficiency of a DD motor, make the wheel smaller. That is the big reason I don't ride that monster bike anymore. The next bike I made for touring is this one. The 20" wheel is slower, so more efficient, but it's also more able to get up a hill efficient, with a big load, because it's simply in a lower gear.