I have a set of H&R coil overs on my 2005 GT now and love them. I installed all 4 corners in about 3 hours and drove it to an alignment shop and have had no problems with clearance at all. Just installed a set of 20's and again no problems.

 

I'm about to do a drop on the rear. plan is to purchase 18's, deep lips, possibly 275/35/18 and want to drop the rear 2". Not sure about the front yet. Figure I'll do the rear first then if I wanna go bigger in the rear can switch rear to the front. But from what I've read and seen coilovers are the way to go.