My Raven Tour "Utillity" bike loaded with the 70 litre Ortlieb Back Roller Pro Plus rear panniers and the 30 litre Ortlieb Sport Packer Plus front panniers.
Font panniers have food, bike rainwear, small toolkit, pump and inner tube, documents and camera for survey use, warm clothing for survey use. The front rack is a standard Thorn low-loader, with a modified stainless-steel rear mudguard and extra stay to the front of the rack (last photo of four).
Rear panniers have waders and survey net (this has a handle that breaks down into 3 lengths for easier transport), 5 litre buckets for sorting and keeping specimens, small observation pots. The rear rack is a Thorn Expedition, which is the strongest bike rack I know about.
On the rack I have white sorting trays, and closed cell foam mats for kneeling on cold wet ground, the latter also reduce rattling from the trays during transport.
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As said previously, I have never used the 70 litre bags for touring, only for transport and shopping.
The Raven Tour frame/forks and racks are rated for a "comfortable" load of 5-6 kg on the front, 15-18 kg on the back.
And maximum recommended load 12 kg front, 28 kg rear, which is about my maximum shopping load.
On a Nomad, the maximum rear load with the same rack would be significantly greater.
For camping, I could theoretically use just the 70 litre rear bags and save about 2 kg, but I prefer 30 litre front and 40 litre rear panniers because:
(i) the load feels more balanced.
(ii) I find it easier to organise packing with 4 bags.
Having front panniers also leaves me more leeway on the back, for example if I want to transport bulky food to avoid shopping for a couple of days, or, more significantly, 10 litres of water in the foldable Ortlieb water bag for wild camping.
If touring and not camping, I do without the front panniers, the 40 litre rear panniers are enough for me, again with occasional overspill onto the rear rack for food and (rarely) extra water.