You can go a little beyond the max. Tire companies put a little leeway due to liability reasons, and because of dingbats, but I wouldn't test these waters too far.
Knobbies on pavement will hardly ever get any flats. I've been riding my mountain bike with knobbies on pavement for 5 years, and have never ever had any flats on them when on the road.
However, I second johnny's suggestion and get slicks...makes for a much nicer, comfortable ride.