Just went thru this same debate this spring. I had 5658's in my Cutlass for about 5 summers. It sat a little low with tall lower ball joints. The ride was firm, not floaty, but almost stockish. It seemed to understeer slightly when pushed. I just swapped out the 5660 springs. This firmed the ride up, and really balanced out the handling with the 5413 rear springs. If it's lowered looks you are going for, the 5660's will need cut.
I just went out and measured my wife's Grand Prix with 5658 and stock ball joints, it's about 7 1/4" to the bottom of the frame, where my Cutlass with tall lower ball joints and uncut 5660's is about at 7 1/2" to the frame rail. It was at 6 1/2" with the 5658's and the tall lower ball joints. Both are probably about 1" lower than "stock", but different ways to get there. I've got the 5658's if you're interested.
I just went out and measured my wife's Grand Prix with 5658 and stock ball joints, it's about 7 1/4" to the bottom of the frame, where my Cutlass with tall lower ball joints and uncut 5660's is about at 7 1/2" to the frame rail. It was at 6 1/2" with the 5658's and the tall lower ball joints. Both are probably about 1" lower than "stock", but different ways to get there. I've got the 5658's if you're interested.