The problem I see is : how a pack lighter than 6-7lbs is going to hold "100lbs or more" (?)
I had a quick look at the McHale site. The two that could do the job are the MBCM2, 5+ lbs , 7,500ci, around 80 lbs (?) or more likely the Super Inex , 7,500/8,500ci, 6lbs +. Both are over $900 with the most basic features.
BTW, I cannot find any reviews mentioning loads carried with the Kelty 6500 but again I find it hard to believe that it could hold (without breaking your back) 100 lbs...
Franco