Hello again Coreman,
I live at 6,000 feet, and have extended family 500 miles away who live at 1,000 or less. I find when I go there to visit, I have tons more energy. Shoot, I can actually run down there.. But the reverse is not true. When they visit us they often feel drained and head-achey for a few days until they acclimate.
When I hunt in the fall I'm often at 8,000 to 10,000 feet, and I definitely feel the difference.