Chimborazo is not an 8K meter peak but it is the peak that's furthest from the center of the earth (because it's a fairly high 6K+ meter peak near the equator). Oxygen levels are, however, a function of height above sea level in a location--temperature is a function of many things--so Chimborazo in that respect is like other 6K meter peaks.
Proximity to outer space is an odd way to put it. I guess the atmosphere, to a first approximation, is also higher at the equatorial bulge.
The atmosphere is thinner toward the poles. The partial pressure of oxygen at the summit of Denali in Alaska (6,000m) is about the same as at the summit of a 7,000m peak in the Himalayas.
Proximity to outer space is an odd way to put it. I guess the atmosphere, to a first approximation, is also higher at the equatorial bulge.