If you're talking about bilstein 5100, they seem to be a popular upgrade. Thought I heard the rears might feel a little stiff.
1. undersized tires / smaller sidewalls means the wheel / tire 'package' itself is stiffer.
Nutro, it's wearing 20" wheels now? Obviously they ride a bit stiffer than the 16" or 17" that it was wearing previously, no?
If you want it to ride a wee lil bit softer, how much more rubber - as in taller tire, for more sidewall - can you fit in those wheel wells?
(Admittedly, 2nd & 4th pics make it look like you don't have room to go taller?)
2. If you want better handling, you DEFINITELY want 5100.
I personally prefer Caprice 9C1 / PPV handling, and am disappointed in myself for buying the 4600 set.
4600 work well, for what they are - they are NOT meant to improve handling / responsiveness.
If you want better ride comfort, you want the 4600 set