I moved from the OEM Bontrager H5 700cx35 to Continental Gatorskin 700c x 28. Moved the pressure up from 70/80 (F/R) to 90/105 psi.

The bike looks great! The ride is a bit harsher, but I can't say I noticed any marked drop in rolling resistance.

I think that you have to go to more road specific tires (Continental 4000?) to see some difference.

On the other hand, the Bontrager H5s at 60/75 psi were riding like a Rolls Royce on rougher asphalt. ...with some penalty in rolling resistance, mainly due to the knobs at the edge of the tire.