When I switched to a Srumpjumper for my commutes, I didn't have the rack installed - I went w/ a Camelback - Their largest modle - found the ability to have it sit a little lower on my back and the ability to connect a belt at the waist as well as the chest secured the bag well.

Center of gravity is indeed higher - I liked the performance of the bike more w/ the weight off the rear panniers, however. I have gotten rid of the Stumpjumper and will be riding a Bacchetta recumbent - I will be interested in seeing how I will manage the load then on my commute to school everyday.

For longer tours I am planning on pulling a BOB rather than using panniers.

Tim