I would look at the lighter Arc'teryx packs. I had a Bora 80 and it was too heavy and didn't fit me right, so I got rid of it. I have tried on this one -
http://www.arcteryx.com/Product.aspx?EN/Mens/Packs/Altra-75#Over_60L
and it fit me better and was quite a bit lighter.
For what you want to spend, you may be able to get a basic custom McHale.
http://www.mchalepacks.com/
Cilogear also makes big packs-
www.cilogear.com
Some of these packs run $1500 at the top end, but start in the range you are talking about.
Another solution is to look for a used Kelty Cloud (out of production for years, made from Kevlar, expensive, even used) Don't get confused by the Red Cloud or similar names. The Cloud comes in two sizes, the big one is around 5000 c.i. if I remember right. Jim Shaw has one.

I don't think most packs are really waterprood. I'd just use a pack cover or put my stuff in light plastic bags if that is an issue.


Edited by TomD (12/16/12 03:54 PM)
_________________________
Don't get me started, you know how I get.