Bill,
I haven't participated in any of the sports you mentioned, so I won't comment on them, but I did own a 625 recently.
I was sold on the "lightning reload" idea of the moonclips, but was very disappointed when I got the revolver. It seems that on my Mountain Gun at least, the chambers were very tight and it was very difficult to reload it fast, since every casing had to be oriented just right for the whole thing to enter. I found it so frustrating that I sent it back to Smith for an action job and to get the chamber mouths bevelled a little for easier entry.
Well, it improved speedloading immensely, although I'm still not sure that it was any faster than just using a speedloader for rimmed casings. I still had to jiggle the moonclips sometimes just like I would a speedloader to get the cartridges to fall in. It certainly wasn't fast enough to warrant dealing with the stupid moon clips, which were not too aggravating given the right tool but just represented an extra step between loading and firing the gun.
In short, I sold it and am looking for a .45 Colt, which I feel is much more versatile in defense and hunting scenarios.
Incidentally, the moonclips weren't one bit any easier to carry on my person than a speedloader would be, and were susceptible (although it never happened) to being bent, unlike a speedloader.
Hope this opposing viewpoint helps, but keep in mind I'm not a competitor like the guys above.