I just compared my H&K USP (full size) to my Beretta PX4 - I was pretty surprised! All the dimensions are essentially the same, width and height, with the USP being only about 3/8" longer. The thickness from the top of the slide (in front of the trigger guard) is very close to the same.There is less than one ounce difference in weight. The USP's girth around the grip is significantly larger although I didn't measure that.
The USP has always looked like a large gun to me and the PX4 more compact; but except for grip girth, they're essentially the same.