Hey guys, if you go to some of the major driveshaft maker sites, there is a lot of good information available on this subject! One of the is www.drivelineshop.com Go to their specsheets section and it tells you the torque ratings of the commonly available u-joints. it says 7260 rated for 400 ft. lbs. continuous torque, 800 ft. lbs. short duration torque, and 1600 ft. lbs. to failure. 7290 #'s are 550, 1000, and 1875.
Dennys driveshaft site also has good relevant info under FAQ's. Lee.