The only option I know of for what you are looking for would be the 55D springs from Brembo50. I have the Eibach pro-kit and I have no issues with clearance. My last car was a G35 coupe at stock ride height and I had to take speed bumps really slow, steep inclines at an angle and could not clear parking stops. I do not have these issues with the Mustang even after lowering, though I still keep clear of parking stops because that one is just a gnats behind from hitting with no passengers. Keep in mind though that if you drop the car all around you will need much more than just springs to do it right. With the 55D springs you will likely not need anything else. Maybe an adjustable panhard bar, but you can keep the factory dampers if you are satisfied with them.
2013 Red Candy Metallic GT Premium Coupe
Black Leather, 6MT, Comfort Package, Brembo Package, 3.55 Axle
Borla Touring axle back, Suntec CXP 45% window tint, Eibach Pro-Kit, Steeda Strut Mounts, Rear Upper Control Arm and Panhard Bar, BMR Relocation Brackets, Energy Suspension Shifter Bushing