I'm still kinda in shock, honestly, at the speed of advancement in standard d20. When we played Age of Worms all the way through, we were at, what, 22nd level after a two years of somewhat sporadic play? If we'd had four hour sessions every week, it wouldn't have taken much longer than six months. Maybe even less.
To me, that still seems crazy. I can't imagine players needing advancement that frequently to keep their interest. Heck, you barely have time to figure out all the goodies you got from your last advancement when you're already having to do it all over again.
I don't really consider myself very aligned with the OSR philosophically, in most respects, but in that one, I think they got it perfectly right. Speed of advancement in 1e and B/X seemed much more reasonable to me. It's almost like you need to divide XP awards by a factor of 4 or 5 in 3e to keep a pace that to me seems reasonable.