Slicks are night and day. My old t28 went from mid 13s to low 12s from street tires to slicks.
You can take a look at your slip at it will tell you almost exactly how much time you'll shave. The car will to from 1.6-1.9 60tfs w slicks. And every tenth of a second you shave off your 60ft will take 2 tenths off your 1/4 mile et.
Also just from looking at your trap speed you can get a pretty accurate idea of what you'll run on slicks...