George, I also messed up, as per your comment;
"For the big four.. I haphazardly bought my first and 2nd rounds of gear.. this time I'm starting with pack. Then I'm going to shelter. then finally bag/quilt and pad."
And I ended up returning or just keeping a few sleeping bags which were too heavy or inappropriate. In the end, it wasn't the most expensive bag which was worth the $ (the original subject of this thread), it was a balance of comfort, space, weight, and cost.
..however, to digress and risk hijaking this thread for a moment, I agree with the previous poster, buy the systems (including sleep system) you need to fulfil your set of requirements, THEN buy the pack(s) sized appropriately to hold it all.
For any readers looking for a way to compartmentalize their purchases, the book 'Mountaineering'*, gives these 10 essential 'systems', which I have (slightly modified) without changing the order:
2. Sun protection
4. Illumination(and signalling)
6. Fire making
7. Repair kit and tools
8. Nutrition(and cooking)
9. Hydration(and H2O treatment)
10. Shelter(and shells)
For now, I have settled on a few packs, depending on the size of those system components. The size of the appropriate sleeping system as per this thread, is a big factor in choice of pack volume..
20 liter range: Montbell Versalite20, 340g
40 liter range: Golite Dawn, 392g
60 liter range: Granite Gear Nimbus Meridian, 1600g
Canyoneering: Outdoor Research DryComp Summit Sack, 346g