300D Turbo at 5,000 feet

[sjh]

When I lived at altitude for a year (~5,000 feet) my w123 300D NA took a significant performance hit.

I now drive a w124 300D (2.5L) turbo. I get 26 to 34 MPG, can travel 75 MPH all day long and have adequate acceleration for city driving. That's at low altitude.

I may move back to 5,000 feet.

How bad is the performance hit going to be?

Thanks.