I would say somewhere between. Dizzy has charts that put the s280 in the 275 -280 range for stock fuel. I indeed was surprised by Hypergrams numbers but was able to get 284 on vdyno with stock fuel at sea level and 291-305 with E30. which actually made sense to me because I was told on stock fuel system I would only pick up like 15hp,
These are all Tune+ tunes on mine.
Though I was surprised by Hypergrams numbers I theorized that it might be possible for Hyper to get the extra 15 or so HP because higher octane as my numbers were coming off 91 pump gas and 91+e85
Is it possible Adam pulls a bit extra out of the engine with his tune? Sure, my first tuner tuned my car on a mustang dyno and numbers looked dismal but the car was not slow. It was a lot faster though after I had Adam tuned it. It also did not toss the codes it was tossing from the first tune.
I will also say HiJinx ( with his current tuner) got more HP on his setup ( non s280 ) at the same rpm that his previous tuner had pulled less out of it.
There are a lot of factors that can come into play with dyno numbers. In the end its all a bit arbitrary . The main thing to conclude is the car really fast. Thats why I think a lot of guys wind up going to the drag strip as it gives them provable performance in quarter mile times.
That with racing known faster more HP than stock cars and beating them which seems to be a big past time for a lot of FiST and FoST drivers in certain parts of the country.