Well, found some new data this morning courtesy of a Slowtwitch post on the new GP 4000 S II — complete with graphs, because who doesn't like graphs?
Slowtwitch: Continental GP 4000 S II (with credit to Greg Kopecky)
Perhaps the most telling bit of interest to me is this graph right here of rolling resistance for various sizes of Grand Prix 4000 S II:
Clearly Continental is on the bandwagon when it comes to wider tires equaling lower rolling resistance, with 120 PSI at 23C being roughly equal to the rolling resistance of a 28C tire at about 85PSI.
Maybe this means I've found my tire.