I have spoken to Saleen about this very subject. The "E" makes 445hp at this time (425 for 2002) due to Saleen needing to make SMOG requirements, and also offering a warranty on the car.
The "E" motor is what now powers the SR, and it comes in 505hp trim.
Without having to worry about emissions, "E" cars with a smaller pulley have made over 600hp.
Most people do not buy "E" cars, and then start to modify them. There is more to a car than the time it takes to travel 1,320 feet from a standstill, and most "E" buyers did not buy their car to think about getting beat by somebody with a GT and a Procharger, as they could care less.
On slicks stock "E" cars have run in the 11s in the 1/4 mile. (11.7 as tested)