Great question, stangin! Lowering your Mustang has a number of benefits, the most noticeable being appearance and performance. By lowering the vehicle, you lower the center of gravity, which greatly improves handling and reduces body roll & nose-dive. Unsightly wheel gap is also eliminated, giving your Stang a sleek, intimidating look (especially over a set of 17”, 18” or 19” wheels).
Lowering kits that are designed solely for performance gains often make big sacrifices when it comes to ride quality, and lowering the car more than 1.5” will require caster/camber plates and a ball joint kit to properly realign the suspension. Considering you want to maintain decent ride quality, I’d recommend the Eibach Pro-Kit; match it with the Eibach Pro-Damper kit or a set of Tokico shocks & struts and you’ve got a great performance suspension without sacrificing ride quality, or rattling your teeth out of your skull!
The Eibach kit lowers the front 1.3” and the rear 1.4” (approximately), so a simple alignment after installation should be all you need to get your pony rolling again. This is the same set of lowering springs that we installed in our 2011 Mustang project car, and we’ve taken that car both to the track and the grocery store. Best of luck with your suspension and keep the questions coming!