I am not always convinced that the mag on a scope is always what it claims to be. Very convincing comments there Rob.
Purely subjective but with my Leup 20-50x50mm at 50x I see 2 bricks-wide at 55yds (very cooperative builders ) but definitely less than 2 bricks wide at 50x on a Nikko 10-50x60mm (Mk3). The image is much smaller in the mind's eye with the Nikko (more looking down a tunnel than the Leup). Also the edge cut-off is very distinct with the Leup, with the Nikko you have to really find the sweet-spot for the optical centre.
The NIkko ranges consistently (but weighs too much) but lacks the fine details I see with the Leup so "focus" means least out of focus with the Nikko but the Leup I can look for the finest detail to set focus (fine aggregate in the mortar between the bricks).
A real test would be to capture the images and run them through a Fast Fourier Transform (FFT) when viewing a suitable test picture and comparing the frequencies reproduced. There is likely to be a difference in the finest detail vs. greatest contrast which is the sort of subjective preference that may vary between shooters.
The one thing I have noticed with my Nikko is that even a tiny turn of the eyepiece can mean quite a marked difference for the side-wheel indication hence I tape the eyepiece adjustment ring. The Leupold is much more tolerant. The choice of eyepiece lens and the way that interacts with the eye/spectacles, etc may have quite an important role in user choice.
I am of course very happy to give a March a go if someone cares to loan one to me :-) [I would love one but wouldn't buy without an extensive test].