If you want the ability to rotate your tires, then go with all four the same. I have found that 255/60R/15's look great on a '69 Charger. I have 15x8 magnums on my Daytona and they fill the wheel wells rather nicely and give a great stance. I've never had issues on tire rub. Now, if you want a slight rake look, then maybe 255's up front and 275's in the rear...