I am a big fan of the "Three Day" style pack for a B.O.B. if you can make due with 2000 - 3000 cui (depending on the manufacture). Lightfighter carries various makes and models of this style pack.

As for bigger packs and heavier loads, I have found that what works for one person can be murdous to another. Although, a full 6000 - 8000 cui pack is going to hurt when carried all day, a good pack goes along way to making that effort less painful and thus increasing how far and fast you can move.

I personally like the Mystery Ranch System. They are hard to find, but are exceptionally comfortable and stable mostly due to the adjusatblity of their design. Although their website: Mystery Ranch doesn't show the older frame design I have their new designs look promising. I have carried some pretty heavy loads over some brutal terrain with good results with mine.

My advice would be:
Figure out how much you want to carry (max load). When you pick a pack, choose one that a. fits you well, b. has slightly more capacity than your expected max load, c. choose a pack or system that allows you to organize your equipment so that it is accessable without unloading your entire pack.