I would never go lower than my Pro kit. I have long tubes, and a clearance robbing intercooler also, and my Pro Kit already causes plently of clearance issues. Depends on what else you plan to do to your car in the future if you can scarafice so much ground clearance. Oh, and depending on what kind of power you want your Stang to make - the more you lower your Stang the bigger your traction problems are (less suspension travel). Makes a big difference. You can't have both there for sure.
That being said. Yes the sportline looks a little better, but it's not anywhere close to being worth it to me. Besides I'm plenty happy w/ my Pro Kit anyway (definately better than stock).