Here's a variety from over the past 8 or 9 years of dyno pulls.
A same day, same car dyno comparison (on a Dyno Dynamics) of the stock exhaust vs. MRT header and midpipe with stock muffler:
Then added Cobb Stage 1 heads and Street cams, still with the MRT exhaust, stock intake, and no AFR tuning. Still on the Dyno Dynamics dyno.
I then added an Injen CAI and tuned the combo with an S-AFC and eventually replaced the MRT header with an OBX header. This shows runs from a couple different Dyno Dynamics dynos, bone stock (well, with a K&N panel filter) vs. Injen CAI/OBX header/Cobb Stage1 heads/Cobb Street cams/S-AFC:
Note that the engine was putting down 50% more power than stock at redline - pretty damn impressive!
Then the same modded combo from above but on a Dynojet:
On a later date it put down 168whp with the same combo - that's the highest I've put down.
Pulled that engine to mate the Cobb heads and cams with a Phase II shortblock with higher CR. In the meantime, in went a stock 2.5RS engine, which died shortly thereafter, then a used JDM engine off Ebay.
Here's the JDM EJ25D with stock HLA heads and cams + all the same stuff from above (Injen CAI, OBX header, S-AFC), now on a Mustang Dyno. This is also with a reclocked ECU that raised the rev limiter by 10% to 7150rpm:
I have some more Mustang Dyno runs but I need to get the data compiled to better show the comparison.