Good question, the answer is rather complicated. I hope I have understood what you are asking...

First Mean Sea Level (MSL) is usually defined as the average height of the ocean at a particular location, averaged over a 19 year period. This occurs at an elevation of zero. As you probably know, as a general trend, increasing elevation corresponds to decreasing pressure.

Is your question possibly this: How low of a pressure can a vacuum pump generate at different elevations? This is an interesting question.

Lets think about the extremes. Say we have a mediocre vacuum pump that here in Santa Barbara can produces a vacuum in a small container of 10 Torr (0.014 times our ambient atmosphere, which is 735 Torr). The SAME PUMP, at a higher elevation of Mt. Everest where the pressure is only ~230 Torr does not have to work as hard to produce a vacuum of 10 Torr in the same small container. Therefore, it might, depending on the pump, produce a different (lower) vacuum such as 5 Torr.

So, in general, a vacuum pump is working to push gas (usually air) from one reservoir (a small closed container) to another (the atmosphere). This creates a pressure gradient that favors the gas moving back from our atmosphere into the vacuum container. The pump must work AGAINST this pressure gradient. At higher elevations, this gradient will be smaller, given the vacuum pressure (in the small containers) are the same. Therefore, it is likely that identical pumps could produce a lower vacuum at higher elevations. Think about even higher than Everest, SPACE! Here there already is a vacuum, so a pump doesn't have to work at all. But, it also doesn't have any gas to push around does it!

Read more about vacuums at
vacuum
and
vaccum-pumps

Hope this helps!