Since the .338 MX has .376 Steyr and 9.3 x 54 as parents,
...and the .338 Federal comes from .308;
I'd have a lot more sources for brass with the Federal,
and a lot more Handi barrels would be suitable for rebores.
So the Federal is probably a better choice for a Handi Project.
...Once again, Dinny has thoroughly studied the options
...and made an excellent choice.
...but that leaves my new lever gun an orphan.