Having the right valve springs INSTALLED AT THE PROPER INSTALLED HEIGHT is very important. Having weak springs is like leaving a good party at 10pm- you miss half the fun!
80 lbs on the seat is actually quite good for stock. I've seen them as low as 65 lbs quite a few times.
A mild performance flat tappet usually does fine with about 100 lbs. on the seat. The RATE of the spring doesn't need to be very high- around 300-350 lbs. per inch is fine. I haven't measured any Z28 springs on my bench but a similar aftermarket spring would be the Comp 981 spring. It checks in around 105 lbs. on the seat with a 323 lb/in spring rate (stock diameter, so it's a drop-in replacement for stock, as is the Z28 spring).
1990 454SS pickup. Original "tow truck motor" 454 upgraded to something a little more "aggressive." Seems pretty stout but the fuel bill is nuts.
78 Malibu. Inherited with only 35K on the odo! Mild 383 with Weiand 142 blower on top. Mid 12s appears to be the best it's gonna do on street rubber. Runs so good I may never drive it again.
"Last remaining QJet tuner on planet Earth!"