I use an Arcteryx Khamsin 50 - 3000 cubic inches - they don't make this particular pack anymore, but do make some similar. I find it has enough room for a three day technical climb with some careful packing and my sleeping pad and helmet on the outside.
The waste-belt is comfy, but a real pain when worn over a harness. I had some gear loops added to the waist belt when I had it in to repair a tear in the bag. I haven't had a chance to try them out yet.
I agree with CBS & Trask - the 4300 cu in is to much.