Sorry, but I have to interject on this one. If you did not see a boost and/or performance increase, something is wrong. Regardless of elevation, spinning the blower faster will increase boost (to an extent) and it will cause it to come on sooner. Top fuel cars crank the boost up by changing pulleys when they run in Colorado because of the thin air (actually, there is the same oxygen content, the higher elevation means lower pressure, NHRA coverage this past Sunday did a good storey on explaining this) so the same principles apply here. Now, on the flip side, if it is 100*+ then the increased outlet temperatures may be causing you to hit on the knock sensor and that would account for a lack of notable performance increase. Better intercooling and/or higher octane fuel would help improve that situation.
Paul