Personally have a good half dozen front and rear racks that were installed and tested with a variety of loads.
Specialized Six-Pack front rack
OMM Cold Spring front rack
Axiom low rider front racks
Specialized Rear Rack
OMM Cold Spring rear rack
Axiom Journey rear rack
Velec rear double tier rack

Have used these on a variety of bikes with various sized Arkel and Voyager bags, various Seal Line Dry Bags and /or a couple hard-shell cases and a handlebar bag in various combinations. If I had only one choice - I'd drop the rear bags and go with just front panniers and a bar bag. The bike tracks better and the weight distribution is easier on the rear axle - which already carries most of your own weight. It may not be ideal aerodynamically, but anyone worried about aerodynamics while cycletouring probably needs their priorities reaccessed anyway. A car is faster, more aerodynamic and has a higher load limit - not to mention a greater range between stops.

The Specialized Six-Pack is designed to go to the corner store. It won't keep panniers out of your spokes, and the load rating isn't high enough for panniers anyway.

The OMM were the most expensive and not all that rigid once loaded to their limit, although the front was better than the rear.

The Axiom rear rack was the least expensive, has the highest load rating and was the most rigid when loaded. The front was also good but I saw no real advantage of a low-rider over a platform rack, particularly since several front platform racks have supplementary rails so you can pick a mounting height for the panniers.

One of the things that was interested in testing was downhill stability at 50kph with loaded panniers on smooth roads. I'll take the load up front any day. On rough roads I'd suggest keeping the speed down anyway - both in the interests of control and for the reduced stresses on the racks, axles and pannier contents. I like to have fun, but no destination or trip I plan has ever been more fun when treated like a race-course.