the advantages are minimal in that sense...specially as you will be running a road tyre. Basically 10mm bigger each side but also an increase in tyre wall size. Add camber to the equation and you are prob worse of with a 255 over a 235 but then again it depends on what you want to do with the car aswell....
im sure the tyre shop will allow you to test fit with a 255 when the rims come in. That would be the best thing to do