Scott,
Here is another factor to throw into the mix:   Calibration of the MP
gauge.  A gauge that is off even a little can make one system look a lot
better or worse than another.
I own two different MP gauges that did not agree with each other.  Using
annually calibrated test equipment, I determined that one was right on
and the other was way off.(both were new, so much for assuming
new=calibrated)  
A gauge of unknown calibration can still do a good job showing the
before and after comparison of an aircraft mod.  I just wouldn't put too
much faith in the absolute numbers.  A small discrepancy in the MP
reading could easily be misinterpreted as a large loss of dynamic
pressure recovery.
So many details.....
Chris Zavatson
N91CZ
360std, 900hrs