Hi,
If I were using a large fluted pan, I would bake the cake at 35o for about 50 to 55 minutes or until toothpick inserted in center comes out clean. Here is a link to great tips for baking at high altitude.
http://www.bettycrocker.com/tips/tipslibrary/baking-tips/baking-cooking-high-altitudes?src=SH
Good luck!