It's a tough call Chris, and it depends on the car. I've seen LS1's running anywhere from 13.2-14.5 in stock form. I'd personally do a few bolt-ons with the LS1(catback, lid, programmer) and a big shot on N2O. They respond crazy to the juice.
As for the Cobra, the first thing I'd do would be gears! They strive on the upper RPM's, and some 4:10's will keep it up there in the power band. Ofcourse I'd throw some N2O at it like I would the LS1, but probably not as large of a shot.
It all boils down to what you set your car up for. Both cars are considered pigs in the auto-x scene, so I personally wouldn't set them up for anything but straight line performance.

Mark

2000 Black CSVT 3.0L Hybrid - 206fwhp & 195fwtq