255 is pretty much the max for Dart's with the stock spring location and stock wheel wells, and those won't work for everyone without trimming or rolling the quarter lip back for clearance. Some cars can, some can't and the backspace has to be pretty much perfect. I wouldn't even go quite as far as saying a 245 was a sure bet for everyone, but it's definitely a safer bet with everything in the stock locations.
275's are the max with the 1/2" spring offset, and even those sometimes require some quarter lip trimming/rolling.