"Is it basically like an Ion in proportion and size, but with a rolltop closure?"
Not exactly. I have a long torso so it might look smaller than it is, but with the rolltop closure only rolled down part way, the pack seems to be larger than my Osprey Hornet 32. I'd guess it's around 35 liters, so a decent bit larger than an Ion. (the Ion was 25 liters correct?)
"Its not the base weight that matters though, its the weight with food and water."
That is absolutely right. However, even with several 5 day trips in the past two years, I have not once completely filled my Golite Quest. The Golite is huge at 72 liters and is really excessive for the trips I normally take. I do love the pack though, and am certainly keeping it around for winter skiing and hiking.
"Looks great, I'd suggest holding off on cuben for a bit."
I was planning on doing just that. Not only is the cost of X-Pac better, but I am somewhat intimidated by the concept of taping/bonding the pack.
My plan for the pockets was to make a wrap-around pocket similar to what Chris Zimmer has done with many of his packs with a shockcord drawstring at the top to cinch it up.
Edit: If anyone is interested the the pack's pattern, you can find it at my new blog here: Mountains Calling