Arkel “rollpacker” 25L?

[LeoBurns]

Opinions? 25L vs an Arkel 42L pannier set up?  With the understanding that with the rollpacker I’d also use a Revelate XL sweet roll. 

My intended use is single un supported touring on a car on fork road bike (rear panniers and rack - all good).... but “if” I could visualize a packing list for the rollpacker/sweet roll (+ a frame pack?) I could reuse this kit on my 29’r MTB, retire the Bob trailer and have a Great Divide set up... common components (different frame bags).

What would I have to give up on using this set up for my road bike (ie Blue ridge parkway tour)?