Magnaflow had a hard time getting above 300rwhp with an exhaust change... on a 2010 (315bhp rating and a much better factory tune), etc.
Again, no one is arguing what a motor can or can't do, rather that the correction method you are implying (8% as "normal") simply isn't accurate. If a S197 mustang was rocking 280RWHP, she'd turn a far better time than a low 14 in the quarter. In reality, the S197 mustang puts down around the low 250hp mark (fordmuscle pulled the same number) which falls directly in line with it's power readings.
That is your statement Maxx. I posted the track times because they are well beneath what you are stating here. There are quite a few more threads on other forums where people are running 13.5~13.7 with 3:31 gears and 3:55. So yes dyno numbers...blah blah blah. I am not going to jump into that convo, but I will still say, no matter what the dyno says, that is just a tuning tool. The track is what matters.