FIGHT FIGHT FIGHT!!!
Here is a chart of pressure drop vs altitude for standard temperatures ...
charty goodness ... however, turbochargers can compensate for this pressure drop by forcing more air in, so you will not see that kind of pressure drop like an n/a car would.
When I was hanging around at cobb waiting for them to finish my install, I asked them about this, and they said at SLC altitude, which is within a few hundred feet of Reno, they see about 0.5 psi less boost than sea level, so for Reno their stage 2 target boost is about 15.3 +/- 0.5 psi.