Brakes...or lack of

[Shug]

You can't really just tell how long the discs have by mileage - need to measure them, they might have tons of meat left. Also, most people wouldn't call cast irons an upgrade unless you're tracking to the point that the MMCs can't handle the temps. Most people won't get to that stage with a standard car and the benefits of MMC (lighter weight, much better dry stopping performance) mean you'd want to hold onto them as long as you can.