OK a few things, the mach 1 and Gt DO have different pistons, if you are running a GT 2001 and new you must change the pistons and rod if you plan on running any more than 8 psi. In 01 Ford started using a softer material in the pistons and rods, which was causing a problem with cracking the pistons, a BIG problem. I am running an 8 psi 3 core ATI and when I bought it they told me that this was such a big problem they would not warranty anything on the kit if I ordered it for more than 8 psi. I personally love the centrifigal s/c. I can launch my car exactly like stock @ 1100rpm and it sticks and takes off like a bitch, I hit 8psi@ 2400 rpm and from then on its woooohhhhhh. I have not had any experience with twin screw chargers so I do really have much info, but I can imagine if you have instant boost then you are deffinately going to have a bit of a traction problem @ launch. A lot oh and the best price for the kit I got is on the web
www.Superchargers4less.com the guys name is Mike. My kit is a stage 2 3 core intercooler on 8psi and it cost me a grand total of 3491.50 to my door; the only thing extra I had to buy was copper core plugs and 42 lb injectors from steeda for a grand total of 310.00 to my door. Hope this help some. And sorry for the long ass post.