4.0 Whipple - Header vs Manifolds
Manifolds/Cats/Ford Racing Exhaust = 735whp @ 23.3psi
Headers/Ford Racing Exhaust - 785whp @ 21.7psi
All other supporting mods the same.
YMMV
http://www.bridgetogantry.com/blog-did-lambo-fake-that-laptime/
and if you need a good laugh (besides VAG pulling another fast one), see this:
https://www.youtube.com/watch?v=9kq3fJmQLok&feature=youtu.be
US allocation corroborated here: http://autoweek.com/article/car-news/will-us-receive-just-100-ford-gts-2016?utm_source=DailyDrive20150923&utm_medium=enewsletter&utm_term=headline-top&utm_content=body&utm_campaign=awdailydrive