I have been going through this very thing for the past year. Been a commuter for the past 40+ years typically carrying a load of 20-30 pounds. Very little sway with this level of load using a Blackburn rack from the 80's. The Jandd panniers I have are about 28 liters, and the Jandd h-bar bag is their Touring Bag and holds about 13 liters, and I find that I need about 10 more liters of capacity for a cross country tour that I plan to do in a few years.
Since I already have reliable and super tested from hours and hours of commuting panniers and h-bar bag, I don't see the need to purchase new panniers. This is what I have come up with. Fork mounted cargo bags. I have made my own cargo cages that mount to the fork and will be getting the bags from a supplier. Unfortunately Jandd has no plans to make fork bags in the 5 liter size any time soon, thus I will find a cheap alternative.
One thing to note. On the Jandd website they have listed a Pannier Pocket, which straps to the pannier. It will also work as a fork bag from what I see. One unique and in my eyes, excellent feature is the bag uses a zipper. Brilliant from where I sit as it will allow me to stack items in a specific order and access them by moving the zipper (two way zipper) to where items are located in the bag. Instead of emptying the contents of the bag to access what is towards the bottom, I will be able to move the zipper directly to the location and open it up to get to the item.
Anyway, this week I will likely order some cheapo fork bags for testing the DIY cargo cages.