Ummmm....
PMs stored in DB add weight to the DB and slow down all DB operations.
Come on Pescado, you know as well as I do that that statement is complete and utter BS. More PMs only affects the size of the PM table itself. It has absolutely zero bearing on the rest of the database or the site. The only thing that more PMs could possibly slow down is the actual PM inbox listing itself. The vast majority of members on MTS2 have less than 5, and all told the entire PM table is 412,657 rows. Does it slow the site down? Nope. Only if you have a very badly configured mySQL could this even *possibly* have an impact (and even then it's extremely limited)... and we both know that my mySQL skills are a hell of a lot better than yours.
I don't mean to be difficult but using this as an "excuse" to have miniscule PM inboxes really doesn't fly. I thought that this was going to be a clone of Insim and setting excessively small PM inbox sizes really isn't anything to do with that. Cutting back the limit really has no bearing on make the site faster - it's just something the so-called "leader" decided.
For creators, having such a small PM box (which is used for both sent and recieved messages) can make it very hard to organise things, or to allow them to be asked permission, etc for items. You know, things that PMs are actually valuable to be used for and stored. Putting your own artificially low limits (with a damn poor excuse of why to boot) isn't the best thing to do for this site.