I wouldn't sweat it. The mixture control is at least 10 times more important than timing control for driveability with altitude shifts.

I regularly travel from my home base 3700 ft, over Wolf Creek Pass, to Lakewood, 5900 ft. Getting the A/F right is the most important thing. Getting my carb jetted to run at altitude has made a huge difference.

If you were doing dyno runs at the different elevations, you may want to check the effects of timing. But in driving, as in just driving from one place to another, I wouldn't worry about it at all.

R.