[91LX2Bfast]

I wouldn't get a roots blower,thats even if the make them for your application. They are great for low boost street use, but lack the power making ability and effiecency of the two other blowers in higher boost applications.
I would go with a screw type charger because it develops boost in the same quick way as a roots, but is more effiecent and can produce more boost if you ever want to upgrade in the future. I agree with you in that your car could use the low end output that only the screw type will give you. A Kenne Bell will turn your Cobra into a Vette Killer. Add a big MAF and H or X-pipe pipe with that blower and I don't see why you couldn't pump out mid 400 hp levels. Then, a better fuel system after that, and you'll have over 500+hp and easy 11 sec time slips.
The centrifugal's are great blower's and can produce some killer HP #'s, but on the street you are going to have to wait for boost while that LS1 with bolt's on's is already pulling on you. If its a car that see lots of track time, then I would recogmend the centrifugal, but since its a street car, I think the Kenne Bell is a perfect choice.