I have been riding 2up, fully overloaded, on the regular PR2s. That means I load the hell out of the bike and ride hard. The wife and I weigh in at about 450 pounds and carry over a hundred pounds of gear. I am on my fourth set of PR2s without a single problem. No shakes or wobbles, no problems at all. Rode to Nakusp and back then put another 1000 miles on so far this week.
I have faith in these tires. I was riding twisty, tar snake covered roads today at way over the posted speeds. Like taking a 35mph corner at 50mph, 2up, while programing my gps with my left hand, Terri was taking pictures.
No worries, just get some tires and ride the bike.
EDIT: this is my fourth set of PR2s and averaged over 10K miles on each of the first three sets.