Technically, neither is "more powerful" or "better." Kv numbers simply tell you how many RPMs the motor will spin per Volt of input power. The maximum current and voltage/cell count ratings are what tell you how powerful the motor COULD be, if you take advantage of it.

Given the same battery pack, the same gear ratio, and the same prop, the 5400 motor will "be more powerful." That is, it will spin the propeller at a higher RPM, generating more thrust and a higher forward speed for the airplane.

You can also adjust the gear ratio so the 5400 spins the same prop at the same RPM as the 4100. Then they're both equally "powerful." You could also adjust the propeller size so the 5400 draws the same Amps as the 4100. Again, they'd be equally "powerful." You can also put a bigger prop on the 4100 so it draws more Amps, and make it "more powerful" than the 5400.

If you poke around, you'll see many reports about Himaxx and Eflite Park 370 motors with fractured magnets. Many/most, if not all of these are the 5400 Kv versions, and many/most, if not all were being run on a 3S LiPoly. The no-load RPM of the 5400Kv motor on a freshly charged 3S LiPoly (12.6 Volts) is 68,040 RPM! Sixty-eight THOUSAND RPM, on a $50 motor. It's just not going to take it. We're talking jet turbine speeds. With a prop to load them down, they do run at a reasonable RPM, but people just can't resist revving the motor up that first time after the connections are made...