Anybody have an experience with both?

I purchased a Compact and got it in the mail today.
It will hold a 3L bladder, a camera, spare lens, and flash, with enough room for my 1st aid kit, but that's it. And that packed its not a great fit. I'd like to have enough room for a rain jacket etc, but the compact is pushing the limits of how much I want on my back. I'm wondering how much more size the Probody is. The specs say 300 cubic inches, but sometimes those numbers dont tell the story.

Would I be better adding a frame pack for excess cargo? I'm a coach for a Highschool team so I carry a lot of junk and use it regularly on the trail.