I bought a 629 Mountain Gun four years ago to shoot .44 Specials in. I made every round it ever fired since S&W test fired it, save a few chrono-ed Blazer 200gr GDHP .44 Specials and UMC 180gr JHP .44 Magnums (Hot!). I loaded mainly .44 Specials and Russians for it, as it was nearly perfect for them. Then, as I started reloading .44 Magnums to at best a moderate level, I found it's real calling. Ultimately, I replaced my 6.5" 24's with a new 6" (partial lug) 629, sporting the S&W .500 Magnum Hogue grips when I need 'emphasis', something I had a .454 SRH to do for many years. Ultimately, I replaced my 629MG with another new standard 4" 629, at only 2 oz more. While it shares the same hammer, trigger, and sights with it's 6" sibling, it does, oddly enough, differ from it. It's uncanny... I don't know which I'd keep, if one had to go.
I guess the 4" is more utilitarian - home defense, car defense, and woods carry are it's forte. The 6" is a great bullseye gun - fine for silhouettes, too. If I were to hunt, it'd get the exposure. I have a myriad of ammo I've made for both of them, and few rounds are real hotties. I find a 300gr LSWC at 800 fps from my 4" to be comfortable - even at 900 fps from the 6"-er - as all day plinkers. There is something about a 300gr .429" LSWC spanking a metal plate... even at 800fps. With those .500 Magnum Hogue grips, they are fine for all day use. Some days I just feel like a 240gr LSWC .44 Russian, barely breaking 700 fps and super mild, for fun, knowing it easily makes 'major PF' . The 629's are nice... both of mine now are newer models with The Lock, a non-issue here.
I also have a 4.6" SS SBH in .44 Magnum, which, brand new and uinfired by me, got a QPR Bird's Head Grip fitted. Super fun plinker... I did 'try' some of the hot UMC 180gr JHP .44 Magnums with that BHG - wow! It normally pushes that ball-like grip into your palm with recoil, and the muzzle flip causes the slick ball to rotate excessively in your hand, resulting in the muzzle ending up skyward, like an AA gun. With moderate .44 Specials and Russians, the grip is super, hot rounds, it is an experience. I like the SBH, but I'd still suggest a 4" 629 first. Good luck!
Stainz