Not a lot.
I own a couple pairs, suede tournament lows in 41 and the fit fine, if a littler tight in the toe box. However a 41 in achilies tore my heels to shreds. Very painful. So 42 in the achilies seemed to work fine, but no massive gap in the toe. Seems I'm a little all over the place with shoes as I'm a 42 in GATs but even they feel like they could be a little tight if I happen to be wearing thicker socks. However I'm an 8D/8.5D in Alden Barrie.