I'm no expert, but I'll chime in and hopefully someone will correct me if I offer any bum data:
The 3" 625s I've seen are the -3 variants, with a hammer-mounted firing pin. AFAIK, the 3" versions weren't made for very long (maybe a year?), so they're rather scarce, and may bode well for its resale value.
OTOH, while the 3" barrel would make the gun a better carry gun, it seems to me the biggest devotees of .45acp revolvers generally use them as HD, range, and competition guns. As far as the latter, competitive wheelgunners generally prefer the max barrel length allowable for their discipline, i.e. 4" & 5" for IDPA & USPSA, respectively. As such, 4" and 5" guns generally seem to sell well, but one with a 3" barrel might appeal to a smaller market.
FWIW, I have a 5" 625 with the lock and MIM parts. Maybe I overpaid, or maybe, as suggested above, 4" and 5" 625s are more desirable by more people, but I paid about what your seller is asking. I wouldn't call it a bargain, but not a rip-off, either.
As far as moonclips, my 625 isn't my most-shot gun yet. It'll be my USPSA gun, and to that end, I already know moonclips are the way to go. Loading them seems like a hassle, but then again, it's really no worse than loading a bunch of speedloaders. The difference is that I can pre-load enough moonclips for the entire match in my garage, rather than spend time between stages reloading speedloaders.
As far as the actual reloading of the gun, many will opine that "moonclips are faster than speedloaders", implicitly suggesting that merely being in possession of a moonclip-fed gun will guarantee fast reloads. It will, to the same extent that merely owning a piano makes you capable of playing Mozart. Whether you use moonclips or speedloaders, practice is what'll make you fast. There are plenty of speedloader guys who can smoke plenty of moonclip guys on their reloads.
