True the .338 can handle a bigger bullet, but the .325 shoots a little flatter with slightly less recoil.
If you re-load, then availability of bullets/cases becomes moot. I would get the one I wanted or liked best based on the actual gun you choose. Getting good results out of a buddies T/C Encore in .325WSM. 200 gr Accubond 69gr 4831 and 2900fps.