I had a similar set up, two panniers in the rear and an Ortlieb medium handlebar bag. On my last two long rides, CrossVermont & XNHAT, C&O and GAP, I broke spokes on the rear wheel. This is on a rigid mountainbike and I weigh 210 lbs. The C&O broke the wheel bouncing down a single track detour around the Paw Paw tunnel. Granted the wheels may have been trued incorrectly. But the new bike is going to be set up with front panniers to distribute the weight evenly. I also found the front end very light with most of the weight in the rear.