springs will most likely be stiffer, varying by manufacturer as said above. The ride quality may suffer but again as said above it is all about the combination you choose. I personally noticed a better ride on my 03 when I did my shocks and struts but I had factory components that had 100k on them beforehand.
2003 Redfire V6,
Show: Smoked everything, cobra front bumper, gt rear bumper, rear decklid and lower valence blackout with black mustang letters, 5% rear front 15%, black 98 Cobra rims front, 95 Cobra R rear black with chrome lip, black scoops and spoiler and exhaust tips
Go: CAI, True Duals with flowmaster super 44's, Bama Tune, full suspension (lowered, 8.8, 4.10s, UCA, LCA, springs, CC plates)