You have your criteria set - 4" for IDPA vs 5" for serious plinking. They both 'seem' front heavy to me... but my first S&W was a 625 Mountain Gun in .45 Colt. The MG's have the nice tapered tube, partial lug, and chamfered cylinder - with a gloss SS finish - really more 'traditional' looking than the other 625's. Don't get me wrong, that 4" 625 I bought some fifteen months ago has since probably sent more rounds downrange than my other S&W's combined... it was my 'competeition' plate gun... where I learned how bad I really am... but, who cares... it was fun!
Oops... that is the key! The 625's are true 'big-bore' sixguns... and you can buy .45 ACP's anywhere - even Sunday evening from Wally World! Just try to find a .45 Colt or .44 Special round... The key is simply that a .45 ACP 625 is shootable by anyone. Sure, the 1911 types will argue capacity Yeah, they shoot 7 & 8 round mags... my Glock 21 had +2 extenders giving it 15 rounds of .45 ACP - now, that was capacity! But... you can shoot a 625 more reliably and accurately than an evil-bottom-feeder... and it won't whack you if you hold it wrong. Either size of the 625 will be fun... that is the key!
Stainz
PS Moonclips are fun - remember that.