The biggest reason I don't shoot my 625 in IDPA is IDPA made 5-inch barrel revolvers illegal so rather than pay to cut it down or buy another 625 I just picked up a used $300 Model 10 to embarrass the bottom feeders with.
I find my splits to be faster with minor vs major in either IDPA or USPSA. Especially on close in hoser stages.
My standing reloads are only slightly faster with moonclips. My running reloads are much faster with moonclips fed revolvers but IDPA limits movement so much it does not seem to effect me that much.
I have only attempted a reload with retention a few times in a match. It rarely goes well for me, never as good as when I practice it in the basement. But I have never been to a match that required it. Per the rules, can a stage force you to do a reload with retention on the clock? I didn't think so, but can't find a rule supporting or disproving that assumption.
I definitely agree that moonclips are far more fumble/disaster prone than speed-loaders but my Comp III's have been pretty good to me so far.