The base stinger with the 2.0T puts out 255HP (not sure if crank or wheels) so a stage one GTI would stomp it. Now if you are comparing a GTI to the optional twin turbocharged V6 making 365HP, well then that is just silly.
There is also the fact that a stage two GTI costs less to buy and build then even the base stinger. Well probably anyway. I guess it depends on the market you are located in and deals you end up getting, trim levels and options as well.
Edit: I mean why build a GTI at all when you can just go buy a 911 GT3 for $143K am I rite guyz?