As usual, Sliderule is right: "A drag racing suspension is not meant to corner well, and a road course suspension isn’t good for drag racing. "
Drop estimates are always just that - estimates, and that is from new OE, not 50k mile worn springs. It all depends on the car itself - weight, etc. Comparisons from the 'before' height can be tough since the old springs may have sagged.
IDK if 4th gen springs have any weird tapers to deal with, but they may need to be removed, trimmed and reinstalled until desired ride height is achieved. This is usually done in ½ coil increments because you can always remove more spring but you can never put material back.
For street cars/daily drivers, be careful you can lower the car too much and create clearance issues (speed bumps, potholes, etc.)
I have never researched 4th gens so I don’t know what is out there, but I don’t like poly in rotational applications like lower control arms. Poly will bind (i.e. noise) and wear oddly due to lateral load. It is fine for items like sway bar bushings. The less the car is driven the less poly is an issue. . I prefer solid greaseable bushings. My 77 and Scooter’s 3rd gen have Global West solid LCA greasable bushings with delrin inserts. Zero noise, zero deflection, next to zero impact on ride quality (due to free movement) and excellent wear if greased properly. But 4th gens don’t have stamped lowers, so again I am out of my realm or experience.
http://www.globalwest.net/
Just don’t buy right from GW, their service is terrible. Try Jegs or ATS.