Turbo's can compensate to a degree (as pointed out in the data from Garrett Turbos). At 10k feet you will still see a fair amount less power due to the efficiency range, not to mention a considerably slower spool up time. Turbos spool up faster and can hit the targeted PSI (whatever that is adjusted to) at lower elevations. For example, I did a test roughly 10 years ago with an Evo 8. Up at SLC (just over 4k ft), the car ran a 13.5 s 1/4 mile at 107mph. Then drove the car down to Texas, using the same setup at lower elevation (just above sea level), the car ran a 12.6 at 115 mph. Driving around town it was a noticeable difference in spool time, about 500 rpm sooner. I drove this same car from Utah to Colorado, and around 8k RPMs, the turbo was taking another 1k RPMs to start going into boost.