I had a 629MG for years - replaced it with a standard 4" 629 last year. The benefits include a larger hammer & trigger, red ramp front and white outline rear sight, and a bit more mass in that still partially lugged barrel. The 629MG is 2 oz lighter, at 39.5 oz vs the 41.5 oz of the regular. I did put the .500 Magnum Hogues, which fit K, L, N, and X frames, on the new 629 for recoil help. They pad the backstrap quite well, yet only add ~3/16" to the trigger reach. The MG pictured is actually one of my pair of 625MG's in .45 Colt.
I had a .45 Colt SS 5.5" RH for years - they cannot compare with a S&W for trigger smoothness or accuracy - even with the 625MG's 4" barrel. As said, I now have two MG's in .45 Colt - and no more RH. I looked at the new KRH-444 4" RH (MSRP $780) - I am happy with my new (Literally 2 days old when I got it 4/06!) 4" 629 (SKU #163603 MSRP $869). The grip is an S&W Accessories-only deal - but the best $35 you'll ever spend if you care to shoot real .44 Magnums. As to ammo - anything SAAMI-spec'd will work in a 629, although the RH's cylinder is a bit longer, permitting a longer bullet to be loaded. Don't let the MSRP difference fool you - a big $89 - the actual store price will be closer - that 4" RH is still 'new' and in high demand. Heck, you can't go wrong with either!
Stainz