The design and construction of a tyre is of more importance than its cross sectional dimension in terms of its rolling resistance, so a crappy OE 28mm tyre will likely roll slower than a good quality kevlar beaded 35mm. Shwalbe 'Big Apples' for example have excellent rolling resistance characteristics which compare very well with some much skinnier tyres on the market. You can have your cake (comfort) and eat it (low drag) if you are prepared to fork out for good quality rubber.
Anyoldhoo, the biggest consumer of your energy output at cruising speed isnt rolling resistance, its aerodynamic drag. Changing to a set of tyres just 3mm narrower will have no discernable effect on your speed.