Look at how far back behind the rear axle the kitty-litter and catfood load sits on the Specialized Sirrus (or any other bike with short chainstays). The center of gravity of this 50 pound load is about 4 inches behind the axle.
As I rode home, the bike was fish-tailing and whipping around in a very unpredictable manner. I would not like to do loaded touring on this bike with 50 pounds sitting as shown. You can imagine a fast mountain descent with this tendency to oscillate could easily cause a "death wobble".
Maybe 30 pounds in the rear, 20 pounds up front. But not 50 in the rear. Split it up, or put it all in a trailer. Or get a real touring bike.