I have a little bit of heel strike if I'm running the shorter light duty commuter Blackburn Crossrack with grocery bag panniers. My bigger heavier duty rack allows me to mount them an inch or so further back and takes care of the problem. I also have no problem running Delta Compact panniers on the commuter rack. The chainstays on my Double Cross are only 420mm long, most "touring" bikes have longer ones.

I won't use the Double Cross for touring with more than 35 lbs. or so because the 28/32-spoke road wheels I built for it just don't feel laterally stiff enough to handle more. It is a gas to take out with lighter loads for a weekend though. It's also a gas to take out on the trails from time to time. I recently mounted the bigger rack on a Jamis Aurora which is set up to handle heavier loads. I don't like being without a commuter when I remove the rack and mount knobbies for cyclocross season.