A few other high volume options:

I have seen photos of the 40 liter Backrollers on a front rack, but it has been several years since I saw that. I suspect that it would work best if they were mounted higher than most low-rider racks would mount them because they would hang pretty low. That is a 15 liter gain over the standard front roller panniers that are 25 liters.

Seven years ago I was trying to figure out how to do a trip with more volume but not use a front rack. Reason for no front rack was that I would need my suspension fork for that trip. I ended up buying a pair of the rear Carradry panniers. I do not recall what their rating was but when I got them I concluded the rating was wrong, I think they are about 50 liters. To make a long story short, that trip did not happen so I had the panniers with no trip to use them. Then finally decided to use them on my 2019 trip just to find out how they worked. Instead of my normal front loader panniers for the front, I used a pair that I bought at a garage sale that were also gray, I think the front panniers were 30 liter, add the ~~50 liter in back, I used a smaller drybag on top in back that was probably 20 liters, thus about 100 liters total without handlebar bag. I could have used a bigger drybag on top instead of the blue one. Photo below.



Before I went into the interior of Iceland I stocked up on food, had about two and a half weeks of food on my bike. I had another dry bag between my 31 liter Rack Pack and seatpost. Photo below. I think that is the heaviest I have ever had that bike, food is heavy. Probably about 105 or 110 liters not counting handlebar bag. I usually strap my rain gear on top of my front rollers where it is handy, that is a few more liters of volume.



But, keep in mind that when you put that much weight on a bike, it can feel like a wet noodle.

My Thorn Sherpa is rated for 30 or 35 kg of weight not counting the weight of bike or rider. My Thorn Nomad in the photos above is rated for 62 kg of weight, not counting weight of rider or bike. Thus, about double what my Sherpa can carry. That Nomad in the photos is a heavy bike, built to carry a load and it handled that amount of gear with ease.

My Lynskey Backroad, Lynskey claims it is the heaviest duty touring bike built and has no limit for weight, but I think that is a crock. I like the bike but I bought it to be my light duty touring bike. I would never try to put the weight on it that I had in the above photos.

My point is that you might get the big volume bags, load up the bike, but find that the frame just can't take it.

Djb rides his bikes down hills at speeds that I refuse to try, but he is very comfortable with the loads on his bikes.