I use the MTX DXP bag: https://www.topeak.com/global/en/pro...x-trunkbag-dxp

Topeak claims a 22.6 liter total capacity, if that means anything to you. It holds a massive amount of stuff. I've done minor grocery shopping and brought home two 10lb bags of potatoes in the zip-open side panniers, 10lbs of security chain and padlock, along with ~10 lbs of other stuff. The Explorer rack is rated for 55lbs of carrying weight, and I've never felt like it or the bag was strained at all even with all that stuff riding in it. The Super Tourist rack you're looking at is rated for 66lbs so I can't imagine ever overloading it unless you have a person sitting on it!

The main compartment of the bag has a velcro divider as well as an elastic pouch built into the soft lid, which is super convenient for stowing standard roadside repair stuff (multitool, inner tube, patch kit, etc) without taking any real space in the compartment itself. The bag and panniers are very durable, I don't have any rips or tears at all.