1.5" drop on the C springs, and you always need caster camber plates, no matter what anyone else tells you. The main reason is that while you may or may not be able to adjust the camber back to specs, the Mustang did not come with enough camber adjustment from the factory, and the more camber you can get, the better.
The R springs are not suitable for street duty, the spring rates are super high, and you'd need Koni adjustables just to be able to control them. Even then, it's going to ride like a brick, and you'll get beat up pretty bad on the streets.
I would recommend the C springs because they are linear, which is nice for handling, the ride is tolerable, and they handle great and have a nice stance. If you want a better ride quality, you may want to check out progressive rate springs like the F springs. They still handle decent, but the ride quality is vastly improved.
2001 Dark Highland Green Bullitt [email protected] naturally aspirated on a bone stock 2V longblock
Under Reconstruction for RS275 Drag Radial Class Pushrods and Powerglide Coming Soon If it weren't for physics and law enforcement, I'd be unstoppable.