What
@jwinslow said is what I believe to be reality given the odds of needing 5 full backups and the 85 man roster constraint.
Tressel touched on this in his own way with the whole "speed", "power" classification thing. You can't have too many OL/DL body types on your 85 man roster because they can't really play ST or help out in any way if they aren't in the 2 deep/rotation. You also rarely (knock on a serious sized piece of wood here) have that many injuries on an OL where you end up needing more than 2-3 backups to play (assuming the T/G designation is fungible).
Currently there are 17 OL on the scholarship grid at 11W site. That is an even 20% of the 85 man roster. I don't think it makes sense to go much north of that number and any given year, out of any given 17 guys you are going to have say as many as half of them (7-8) developed enough to be starters or primary backups and the other half either developing underclass types or, unfortunately, "busts".
Another way to look at it is that spread out over 4 years you are looking at an average OL class of 4 guys per year. If you want to have a full 2 deep, almost 3 out of every 4 are going to have to develop to starter quality. I'm not sure that is realistic for any coaching staff given the difficulty of projecting OLinemen out of HS.