For an orange, I would go with one of the softer springs such as any of the Steeda offerings. In order to get somewhat close to my target of .65-.7, I needed to adjust my Yellows up (all four were adjusted to different angles, but as close as I could get to the same rebound without increasing my rebound to compression ratio too much). I currently have a set of H&R race springs on the car.
2014 Mustang V6-Built to run TTB, CAM-C, and ESP
Proving to my fellow racers that the disdain that some GT drivers have for V6 drivers is unfounded, one results archive at a time since 2013.