I'm currently running the Stainless Steel Brakes slotted rotors and matching pads (purchased as a set from Summit.) They work very well, better than the stock setup, but that is probably more due to the pads than the slotted rotors.
I've tried a few low-buck brake "upgrades" including :
-NAPA carbon-ceramic pads on stock rotors ('98 Silvarado). These *seemed* to work great but turned out to be *too* agressive and warped the stock rotors very quickly and very badly.
-Summit cross-drilled rotors and matching pads ('98 Silvarado) worked fine and were half the cost of new GM replacements. No problems on the street, but if you take a vehicle into the mud, *stay away from cross-drilled rotors*!!!! the holes will get packed with mud and greatly reduce stopping power until you clean them up. don't ask how I know
-NAPA carbon-ceramic pads on stock rotors ('87 GN hardtop-sold) exact same experience as the truck (I should have known better) they stopped GREAT! but instead of warping the rotors, the rotors cracked!
-Stillen cross-drilled rotors and matching pads (same '87 GN hardtop) again these worked great. Seemed like an improvement over stock. Never had any problems. These were thicker than the stock rotors which, althrough heavier, would make them less likely to warp or crack.
-currently running the Stainless Steel Brakes slotted rotors and matching pads on my '87 GN t-top. I'd say they were about the same as the Stillen cross-drilled as far as stopping power. But that's a "seat of the pants" measurement, not anything close to scientific.
As a side note, the Stillen cross-drilled looked virtually identical to the Summit cross-drilled rotors aside from the fact they were for two different vehicles. The holes were drilled the same way and the material looked identical with very similar imperfections, etc.
HTH