All hives are different. I installed 2, 2# packages on Apr 20th and 1 hive already has 12 frames filled. The other is working on it's 6th. From what I am told by a local bee keeper, a 2# package having 5 frames filled at this point in the game is on par. My 12 frame hive is simply doing fantastic. So, it would seem that you also have a hive that's doing very well (above normal) and another hive that is just normal.
Also, you should be going by the 70% rule. When 70% of your hive (normally 7 of 10 frames) is filled, then add more room.
About using 9 frames, I believe that is only beneficial in a honey box, not a brood box. It can be counter productive in a brood box? i.e. The cell depth will be deeper than normal but it's just wasted space when it comes to brood, they don't need that much space. Now, when it comes to honey, they will fill the cell regardless of how deep it is, thus you can actually have an increase of honey storage when using 9 frames in a honey super. I hope I am saying this right as I also am a beginner and am just repeating what I've been taught :-D
Jeremy