The black center (i.e., the 7 - 10 rings) of the standard NRA 25-yard slow fire pistol target is about 5.3 inches in diameter, which is equivalent to about 20 MOA. NRA targets for other distances, and also for the timed/rapid fire stages, are scaled so the black is approximately the same MOA, though obviously different in size for the different ranges.
I've been shooting Bullseye competition for about 30 years and currently am just barely holding on to my NRA Expert classification (which is not nearly as big a deal as it may sound - there are lots of Expert shooters in the leagues I shoot with). The point is only that I've seen lots of shooters of varying abilities come and go over the years. Based on that experience, I tend to think of a good shooter as someone who can keep his shots in the black, i.e. turn in 10-shot groups of 5 inches or so, most of the time (slow fire, one-handed). That individual will generally be scoring in the mid-80s or better in the slow fire stage, and in the high 260s or low 270s overall. Very good shooters will consistently turn in slow fire scores in the 90s, the key word being "consistently" - everyone gets lucky from time to time. They are few and far between.