If you look at the strut before installation press down on it to see how much harder it is to push it down than stock ones, you'll see that they are noticeably stiffer. This is why they are performance struts. This is also why you have less body roll. They don't flex as much, making you sway all the time. The springs won't make a huge difference in handling. Yes, they do lower your center of gravity but not enough to have a significant impact. That's just a selling point for the spring makers. Lowering is mainly for looks, most people don't realize that. Lowering springs with their stressful spring rates, will also cause the struts(new or not) to lose life. The ride will be much harsher too. Your car isn't that high of the ground to begin with. A 1-2 inch difference in height won't change too much as far as handling goes. This is why you don't really need springs with struts. But, if you are getting springs, then you have to get better or stiffer struts to handle the extra stress.