I'm looking at turning a pair of 41L and 32L messenger bags that I'm confident I could convert into a pair of panniers for the front or rear wheel, by using the designs of previous folks. Practically, however I'm curious how that kind of load distribution would affect how the it rode and handles, as on the rear theyd be completely above the rear seat stay and extending a bit behind the wheel, and on the front theyd cover the wheel pretty extensively. Conversely, the largest panniers I've seen via searches so far are around half of the capacity of this pair of bags, and are generally much longer vertically, whereas a messenger bag is horizontally much longer.

To summarize, will messenger bags (70L total) work well as panniers if they
(1) are twice as big as a normal pannier set (40L max by my est) and
(2) much longer than they are tall?