The 2013 brake levers will allow a couple of cm extra grip space.
I don't worry about cutting grips down as when I change spacing around I fill the gaps with cut-offs of foam grips. This removes the need for everything to be measured with exactitude and saves a few grams of weight. But it might be worthwhile putting the original grips back on for a few months until the 2013 brake levers are available to buy. They'll increase braking power significantly.