When I finally reached the 10 lb "UL threshold" I no longer noticed the pack and that turned out to be light enough for me. In the three season hiking I do, I like to be comfortable down to 15F and survivable in single digits. And handling four days straight of heavy cold rain is my guideline (survived that, barely, in WA state twice, on the PCT and PNT).
I realized the pack was light enough on my PNT hike when there was a break in the rain and I doffed my rain jacket and stuffed it in my pack without breaking stride. And that was with several days food. After that moment, I no longer looked for any more weight savings. The five-pound "SUL" label is just not going to happen for me. If I never pay for Cuben fiber, I'll be OK with that.
It's impressive and fun to see SUL hikers do what they do, in the same way it's fun to watch world-class athletes excel at their games. I'm an avid recreational cyclist, and I know now I'll never compete in the Tour de France. After a lifetime of hard cycling, I can just sit and wonder, "How do they do that?"