I'm about to pick up my commercial M17 P320 and I want an adjustable rear sight. Does the adjustable part for the 320 X5 or Legion fit the commercial 320 M17? Thanks.

Some or all of the old X-Five's have the sight cut for the older Romeo sight, those would not fit. The Legion is cut for the Delta Point Pro, that should work on the M17 and M18 civilian pistols that use two screws.

I think SIG will be offering an adjustable rear sight in the near future that would be even better, take a look at the rear sight used in the SIG M18X video, I would wait for that sight to become available.