although that statement is vague, a 50 to 45 profile difference can be drastic depending on the tire. I've found the more expensive Toyo Proxes4 do ride exceptional for a low profile wheel. In the name of performance, 15s. The arguement of 'weight' ignores performance of tires as well as the bigger advantage of a firmer, smaller sidewall. If you want comfort, 14s would help and give you access to cheaper, less grippy tires, a lot wider range, but 15s are definatly gonna help if you plan on doing ANY performance driving. Why are the 15s on the back and not the front? Put the 15s on the front as those are what is steering the car. More direct steering feel (albeit firmer). It really is performance verse comfort.