Actually, the weight should not be transferred to the waist (that is not where the pack belt should rest!) but to the hips. The pack belt should rest on the top of your pelvic girdle. It will put the least stress on your lower spine that way, since the weight resting on your pelvic girdle will go directly to your hip joints. If the pack belt is at your waist, it will definitely concentrate more weight--and twisting--to your lower spine.

Pack fit is almost as individual as shoe fit, so I can't recommend one over the other. I personally need a pack with load lifters that keeps as much weight as possible off my pressure-sensitive shoulders. I also have lower back issues, although not quite as severe as yours.

Should I need to look for a new pack (my current 10-year old pack, a long-discontinued model, is just fine), I would first look at the ULA Circuit or Ohm, or at the Elemental Horizons Kalais. Again, those would be for me, not necessarily for you.

You will need to try each pack with the gear you plan to carry in it (plus the equivalent in bulk and weight of a week's food and a day's water). Have this ready when the pack arrives so you can load up the pack (without removing tags) and try it out (probably indoors) before the time for returns expires, being sure to keep the pack clean and dry. Plan to budget for return shipping--it's worth it to have a properly fitting pack, especially in your case.

I'd also get on the phone with the manufacturers you listed and discuss your specific issues with them. They can give you a lot of advice!