I'll tell you that my thought in setting the bench at 6 is two fold: first, it keeps our league in step with the MLB roster size of about 24-25 -- we'll have 9 positional starters, 3 SP, 3 RP, 4 pitchers, and 6 bench players:
9+3=12+3=15+4=19+6=25.
Second, it makes owners make more difficult choices about who to keep and who to put out on the waiver wire as the season goes along. If my choice in thinking about picking up some guy who's on a hot streak or a brilliant prospect brings the consequence of having to drop a pretty solid bench player, I'm going to think much differently about that decision with a 25 man roster than a 30 man roster.
With that, it also gives some opportunities to teams that struggle with bad picks or injuries to recover a bit by finding players on the wire who might help. I think a problem in the last few years has been that teams get buried early and, because of the larger rosters, have little to no ability to make meaningful changes. I'm thinking that reducing the roster size and making the decisions tougher will encourage teams at the top to allow prospects to become available to some of the also-rans or make better free agents available to those teams.
I think it also will serve to make the decision to employ a rotating-door philosophy with pitchers a much harder one to pull off, since owners who do that will almost necessarily have to drop relatively good arms to mill the roster.
I'm still open to thoughts on that or any of the other rules of the league.