20-30hp isn't uncommon. If you see more than that there are usually other mods that came with it, or the car wasn't tuned prior to the headers but was tuned after, etc.
Throttle body size doesn't really matter on centri/turbo like it does on a Whipple. People have gone 7's on the twin 65mm Cobra Jet TB with a ProCharger
beefcake went 9.1 @ 153
Interesting that they did ported heads already. Has anyone flowed the gen 3 vs gen 4 heads? how different are they? cams the same specs?
Think about it like this. An EcoBoost weighs 100lbs less up front than a 5.0, and we all know how much better those handle with the lighter, more nimble front end.
If you add another 100lbs to the front end with a Whipple, you're basically creating a dangerous understeering machine!