You also want to look for a triangulated rear rack - much stiffer. IIRC, the blackburn expedition is triangulated. I have a Tubus cargo. Very heavy duty and very stiff. Love it.
As far as bags go, I would skip either of those and get Ortliebs. I had the cannondales and they lasted about 6 months before I started seeing holes. I, too, commute with a lot of weight - in my case, a very large notebook PC. The Ortliebs have gone longer than that and are absolutely watertight, which the Cannondales were not. Ortliebs cost an arm and a leg, but so does replacing panniers. I *love* mine.