Sailing by yourself, on handicap or small fleet, the difference would not be noticeable. In a reasonable size OD / Class fleet, it is a game of inches when you are trying to sail under or over another after a start or on an upwind. Those inches can turn into many boat lengths if you get spat out.

As Tony_F18 pointed out, there is also a difference in acceleration when graced by a gust. It is more important on lighter boats where gusts will result in more healing motion before accelerating (Boat appears more 'flighty'. Wider beam means the boat will transfer the energy from each gust sooner and more efficiently into forward motion.

Even if you gain an extra 1 foot every gust, it will make a big difference when you are around other boats or coming in contact with other boats further down the course / race.