This is the setup my wife used on a 74 day ride across the US. She used a pair of Ortlieb Sport Packer front panniers on the rear rack along with her camping gear on top the rack. She carried 25-30 lbs on a Cannondale T800 touring bike.
We used to go with lighter loads, and used custom made panniers on our road bikes. The panniers were built with enough taper on the front side to allow centering the panniers over the rear axle with no heel strike. We rode 25 mm tires on 32 spoke wheels, and carried our camping gear without any issues.