I rode a 28c tyres - it just about clear the Campagnolo brakes, whether the 30c Grand Bois tyres doesn't, the maxium clearance those brakes can accept is 28c;
Having said that, when I installed the Marathon Plus 28c, it doesn't clear the brakes, it appear that the rubber itself is quite thick to the point that it's realistically 30c.
Also different width rims can make a difference, with touring wheel, the Grand Bois 30c (the best and lightest tyre out there) fit in the brake nicely, whether a narrower rims doesn't allow it to fit under the brake.
ed - was there room to squeeze a mudguard with the 28c?
ed - was there room to squeeze a mudguard with the 28c?