Ryan Harrell is one of my favorite people to interview. He's so knowledgeable about motors, it just seems like every time we talk I learn so much. And you guys obviously agree, because his videos get tons of views. In case you didn't watch the whole interview, here are some key points that we discussed.
Think of motors in terms of weight and power, not in terms of size. Today, you can buy a 2306 or 2207 sized motor that weighs around 28 or 29 grams. That's equivalent to what a 2205 or 2206 motor used to weigh (and some still do).
A few grams of weight at the end of the arms makes a difference. You might be tempted to shrug off the difference between a 29 gram motor and a 34 gram motor. What do 5 grams matter if the motor is making 1.5 kg of thrust? Trust me. It matters. First because 5 grams times 4 motors = 20 grams, and that's a fair amount of weight to remove from a quad. But also because weight at the end of the arms has a more pronounced effect on handling (especially very abrupt maneuvers) than weight near the center of gravity.
It's difficult to generalize about motors based purely on size and kv. Motor performance has a lot to do with the overall design, including the windings, the stator laminations, the magnets, and the air gap. There is no reason to assume that two different motors of a given size and kv will perform the same. Real world test results matter.
Of course, we talked about a whole lot more so if you want to see it all, check out the full interview here: https://www.youtube.com/watch?v=J-OFDWGztYo