Yup, run the fattest tyres you can - 25mm tyres have 20% more volume than 23s, so make a noticeable difference. Dropping your tyre pressure helps with comfort and grip too.
I rode L'eroica with some 32mm file tread CX tubs on my Gios - I was cruising the downhills and was getting grip on the climbs whilst others struggled on skinny tyres.