I think the next step you should try is the oem intake.
Those things are awful, and are the biggest hurdle to overcome in that combo.

I know of a couple FAST guys who had more serious builds than yours that didn't run much better. All in all...... That's running pretty good.

The other side of the coin is, it shows that headers are still a pretty cheap and effective way to gain performance.
I have to believe if the headers had the benefit of the tti mandrel bent tubing and an h or x pipe behind them, there might have been a little more ET to be had.