I don't think you'll find that much of a difference at 5,000 feet, and you should expect to do that ride! I started my ride to Tioga Pass in Yosemite at 6,000 feet, and didn't notice any issues with my breathing until I got to 9,000 feet or so. Take it easy, and pay attention to hydration - the air tends to be drier up that high, and you'll find you want to drink more than usual.

JB