Chuck,
My first lightweight pack was the Z55 and I still have it and would use it for any trip where I am carrying more then 25 lbs of weight.
I have carried it on the High Sierra Trail to Mt. Whitney for 70 miles over 4 days and it was a dream to carry.
I have since moved on to a GoLite Jam2, which is lighter, but honestly not as comfortable as my Z55.
The biggest decision that I see for you is if you want to take that leap of faith into lightweight/UL and shoot for a frameless pack or not.
My thought is that if you like going light and want to go UL, then YOU WILL end up at some point with a frameless pack.
I am relatively new at the light weight thing but tend to think that you have different tools for different jobs.
So having a frameless and framed pack is not a bad thing.
My friend, Jeremy, used a Granite Gear Vapor Trial on the same 70 mile trip and was fine. It has a frame in it and is 1 lb lighter than the Z55.
If you are looking at the Jam2, check out the offerings by Laurel Mountain Designs. Ron's packs seem like highly customized and lighter versions of the Jam2. (My friend Jeremy just bought the Exodus and it is a beautiful thing that makes me jealous that I did not get one vs. my Jam2).
Anyway, good luck to you on your lightweight journey.
-Tony