A couple of things. One, I don't know how much experience any given person has when I read their comments. Two, I've synthesized my opinions on these packs entirely from product information, product videos, and quite a bit of reading on forums online where users of the packs comment on what did and didn't work. Once again, I don't know how much experience each given person has. Further, two people who each have experience on the subject matter will often disagree due to personal taste. See this thread, for instance, where some people say something like "ULTRA pack on the Icon Pro is a bad idea" and then another guy who clearly has tried a number of packs says something like "I actually like the ULTRA pack on the Icon Pro". As I said above, I asked in the first place so that I might learn of other options or get help narrowing down from what I've found. So far it looks like I've found most of the sub-4 lbs packs. The number of people chiming in that SG and SO are good is reassuring if nothing else. Quite a few people also argue for Kifaru, and I could potentially do that if I made a frankenpack starting with their suspension.
I'll also tell you an anecdote. I went online years ago and researched the hell out of climbing gear. I showed up at Yosemite with zero experience and a bunch of shiny gear. A gray haired guy a little less than double my age said he'd climb with me to show me the ropes. Once I unloaded my pack he was instantly impressed with my gear selection. I had successfully selected a great assortment of gear (in a 2 lb pack by the way, which is still doing great) which he was envious of. Not because he was out of touch (his gear selection was similar to mine but only a generation older), but because I just had the latest and greatest, and it was overall well thought out. I'm not saying I'll get it perfect on the first try, but my experience is that synthesizing the opinions of others via forums and researching via other methods online can lead to decent buying decisions. Usually better than just showing up in a retail store and asking the clerk who may or may not have a clue what to buy from their limited selection, anyway.
I will admit that saying I won't buy a pack over 4 lbs may be a bit extreme (e.g. if a much better pack existed and weighed 4 lbs 8 ounces, it'd probably be worth it), but it'll be hard to convince me to go for a heavier pack when there are well regarded options at or below 4 lbs.
I don't need the pack ASAP, so I'll read up for a bit and wait and see if any 2016 lineups are announced which include new packs. In the meantime I might even research self-made packs a little bit more. I think it would be cool to tailor a pack perfectly to my needs and size. Imagine a self-made carbon fiber frame molded exactly to the user's back... Now imagine it snapping in half in the field. OK, maybe I won't get too crazy.
Based on this thread alone, it certainly appears that you are content to discount the opinions of those who challenge your predetermined opinions. To each his own. I choose to listen and learn. In my experience in helping novices in other fields that I have expertise in, I prefer to work with someone who is eager to learn rather than a know it all. They are also the folks that I am more excited about helping on an ongoing basis. Therefore, when I'm the novice, I choose to eagerly listen and learn. Just like packs, everyone has an opinion. I'm just telling you what works for me.
Once again, best of luck in your search. I hope you find the perfect pack for you.