Noise and temperature
The Corsair duo's fans remain switched off at 200W and kick in at around 350W. The RMx uses a cheaper rifle-bearing fan that is not as quiet as the fluid-bearing models found in the other two supplies. Is it loud? The answer is no, because it produces a consistent whooshing sound instead of a fluctuating high-pitch noise.
The Corsair supplies aren't quite as good at keeping the temperatures in check. We wouldn't expect them to be, frankly.