For me a decent 50-60 litre backpacking rucksack should weigh about a kilogram, in my experience packs that weigh a lot less than this have an inferior frame/harness combination and won’t give you a comfortable carry at my typical backpacking weight of 30-35lbs (that's around 15kg). The Gregory Optic 58 Litre pack just meets this criteria, I was just on the cusp of a Medium and a Large back length and ended up with a Medium, so the minimum weight Optic 58 I could take would be 1104g (the basic pack; lid replaced with top flap). I liked the top pocket so I replaced the flap with the proper lid and it weighed 1154g.
I didn't even consider taking the rain cover at 90g, my view on rain covers is that you still need drybags for the gear inside the rucksack so the rain cover is just protecting the pack itself, therefore unless the rain will be so bad that the fabric of the pack will hold onto water and make it heavier, there's no need to use a rain cover. I had one very wet day where I could see that a dry rucksack would have been much easier to handle in the tent porch than my soaking wet one - but then I would have had a very wet rain cover to deal with anyway. I still wouldn't take one.
The Optic swallowed all my gear and nine days food - the starting weight was a shade under 35lbs, and it felt very comfortable, the hipbelt is easy to adjust and is well padded for a rucksack in this category, as are the straps. The Optic has a stretch mesh back panel which allows a degree of airflow between you and the rucksack, when combined with the very stiff frame that transfers the load to the hips the whole harness system is comparable to rucksacks twice the weight - it's very comfortable and the load doesn’t move around.
To start off with I had too much weight in the lid pocket which did bounce around a bit while I was walking and I learned not to put too much in the top. Feature-wise I also found it to be excellent - I was using a Platypus hoser for hydration which was easy to use with the pack. I really like hip belt pockets which the Optic is fitted with, and the large mesh pocket on the front of the pack was invaluable for wet gear.
There are also two mesh pockets, one on either side of the main pack, these have openings at the top and side (facing front), these are clearly designed to be accessed while wearing the rucksack although I found this tricky and was a little paranoid about dragging an unwanted item out of the pocket while I was getting something else, this could be done easily without realising it resulting in lost items. If you aren't accessing gear on the move then they work fine as a standard mesh pocket, although the compression straps interfere with them - compression straps are another thing I simply don’t use - when my pack is full compressible gear like a sleeping bag or insulating clothing lives in a compression drybag - as my pack empties because I eat the food I'm carrying these two items are gradually packed more loosely taking up the extra volume.
I was also impressed with the fabric used in the Optic, although thin it seems pretty robust, relatively speaking of course, but with care it will not fail and should last a long time.