I had a bit different experience with Swift springs, but that's probably mainly dependent on the quality of roads in your area. You can find more info here
Went from Swift springs to stock ZCP
https://www.m3post.com/forums/showthread.php?t=1452963
As far as handling, my opinion is that changing springs for stiffer and leaving everything else stock will result in less grip. Turner motorsport has an article on this topic, suspension stiffness must corelate with the grip your tires are able to provide, as well as road conditions.
If I didn't have a zcp I would go with Dinan springs.