Yup, like I said it could be my weight but the tail wagging effect is one I'm familiar with when trying to adapt any bike to rear load carrying. CycloCross bikes are nice but they are more for tossing around by a rider than getting tossed round by a load. What I did discover was that there was a noticeable difference between a pannier load (Ortlieb front packers/rollers) on a very narrow rack like the older Axiom Streamliner and a regular wide rack like the Tubus Cargo, Topeak. Same load with two very stiff racks but the tail wagging to the front end was more noticeable with the conventional wide racks.