As promised, here are the comparison pics. The first is a bottom view (L to R) of a SIG P220, Beretta M9, HK USP9, FN FNX-45, S&W Model 28 Highway Patrolman w/4" bbl. These were lined up by muzzle. Out of the semi-autos the Beretta is the longest.
The next is a side view. The FNX-45 with the 15 round mag is the tallest, with the USP9 and the Beretta being the shortest.
Here is a slide thickness comparison with the USP9. The FNX-45 is wider, but not by much.
The last few pics are a comparison with the M&P9. As you can see the FNX-45 is the larger handgun overall.
I chose these specific handguns, because they are full size duty/service handguns so they fall into the same category as the FNX-45. Realize that a USP9 (and the 40) are smaller than the USP 45 variant, so that may have been a more appropriate comparison since the FNX-45 is a .45 ACP handgun. The only handgun chambered in the same caliber is the P220. For a comparison with the 1911, it has a similar length and height as the Beretta, but would be the thinnest out of the above handguns. Sorry for the somewhat blurry photos.