I own a 442 and a 637. I've owned the 442 longer. The 637's 5/8" longer bbl still allows for pocket carry in a Desantis Nemesis with no trouble, although I carry it IWB about 20% of the time also, which presents no noticeable difference either. The hammer does not impede my draw in either case, which is a thumb-placement function.
The real difference is I can keep the 637 on 8.5x11" paper at 20 yards (firing SA) and I can't do that with the 442. Yeah I know, they're supposed to be close-range tools anyway, but I like being more confident in my shot-placement at any distance, and the 637 does that for me. I can't even remember what prompted me to buy a 637 with a 2-1/2" barrel, but I have grown very fond of it, and the 442 just sits in the safe ever since. I think I carried it at a wedding exactly once since getting the 637. I do, however, opt for a full-frame 9mm IWB about half the time also, especially in street-wear. I'm at home on the farm right now and the 637 is in the pocket of my Carhharts, with two speed strips in my back pocket, each has five Rem +P 158gr SWCLHP R38S12, and one CCI shot-load... (... for Copperheads, I hate those things... a neighbor's three-year-old daughter almost lost a leg to one...)