You will get a bit richer, but you'll likely be okay. SUs do adapt to the elevation changes pretty well -- you'll be a little down on power, but should still work fine if you're well set up where you are.
For reference, I currently live at about 5500' elevation. I've had the my cars up to just over 10,000' without any issues, as long as they were working well at home. My Morris is set up nicely, and did great up on those passes. My MGB used to run really rich even at my house, and really struggled up above 10,000'. Rebuilding the carbs and setting them up correctly for elevation fixed all that.