It doesn't get any higher than this in the USA.


Its a little rattly, but what can you expect for 8.5psi air pressure and 28* injection timing.
http://www.youtube.com/watch?v=zSFUj3sr4ek

So how's it perform? Reduction in absolute power? Obviously, there is less airflow at the same boost pressure.
Lack of power? Absolutely not. Even with the turbo "disabled" (vanes open), at 14k feet it still accelerates nicely. With the turbo the power and acceleration doesn't feel much different than at 10k' lower, just a hint of extra lag.

So if you're feeling a drastic loss of power going up only 5000' then your ALDA has a broken capsule, your injection/cam timing is off or your compression is down quite a bit. 5k should be insignificant to engines without a carburetor.

Here is my old wagon with the T3 turbo 7 years ago on Pikes Peak.
http://www.youtube.com/watch?v=QtEvPIBq9OU