Okay, here is the new REI Link II Pannier empty and mounted on the drive side:
It is mounted on the lower pannier rails because (A) it fits there, (B) it gives me a lower center of gravity, and (C) it frees up the top rails for strapping an overflow bag and other stuff (e.g. soggy wet stuff). Since this is the drive side pannier I intend to put stuff in there that absolutely needs to be kept dry and is unlikely to be needed before I get to camp that evening. So things like my down quilt, sleeping pad, spare socks, inner layers, &c.
This is all of that stuff in a big pile:
This is all of it overstuffed into that tiny pannier:
Now that was most everything, but it wasn't a realistic carry because I don't cycle just in shoes, a helmet, and sunglasses. I need to wear some of the clothes jammed into that pannier. This is what it looks like with typical ride clothes removed:
Hard to tell really but I was able to get a couple more rolls on the roll top.
Now in practice I will carry some of that in a dry bag on the front as well. Also in practice there might be some additional small items that ride along (the cable and charger bag is in there, but there might be some other small items).
With the 5L front drybag I can easily pack the sleeping pad and a bunch of clothes forward, which leaves plenty of room in that rear pannier.
The bag looks good but I'm not super impressed with the external pocket.