Yeah, I was thinking about what scriming said. He's right that the bottom of the stock run seems low. But I think even if you ignore the stock run below 3K (where it looks noticeably low) and the headers run above 6.5K (where the run seems to have ended a bit early and clipped the peak) you've still got a big chunk of the power band that shows some really nice gains. I'm just eyeballing it, but it looks like about 12HP and 20TQ on average.
Even if you were to drop in scriming's stock run in place of mine (I know you can't really do it, diff. dynos on diff. days with diff. weather, etc....but just for fun) you'd still see some gains. At 4500 RPM I see about 7-8HP and maybe 10TQ. It's more like 15HP and 17TQ gains at 5K. All that to say, I think these probably are showing some pretty nice gains over stock.