It seems like we have had a running debate about USGA versus other handicap systems.
I have been looking in more detail regarding handicaps and anti-handicaps and came across a page by Don Bender. http://thesandtrap.com/t/45853/the-dan-plan-10-000-hours-to-become/936#post_986626
So, it seems like the charts on a consistent 15 handicap on Figure 5 kind of answers the question for your average golfer.
The average score (running average over the entire data set or statistical mean) is around a 17.5 for this golfer. The difference between a golfer under competition conditions and play for fun in the US is not really that significant, as many of us play for skins or some other "bounty". My guess is that a tournament conditions are more controlled, because there is a fixed time per hole.
So, the handicap difference is only about 2.5 for a consistent USGA handicap golfer rate at a "15" who would be a 17.5 in other countries. Of course, the least consistent "15" handicapper would be about 21.5 within the averaging handicap systems.
What does everyone think about this assessment?