That would make it a hard ride! 25mm tyres are shown to have a lower rolling resistance than 23's anyway, so I know always opt for 25Black Zaffiro 20c's on chain Reaction for £5.99? I'm tempted as they only get an outing each weekend, might be able to make the low rolling resistance case.....!
What about Schwalbe Lugano's 700x23c? Anyone used those before?