Currently the world generation does not take advantage of the full height that was added in 1.2. This means that to see a mountain as tall as the world height we must build it ourselves. Of course this is an almost impossible undertaking and will probably never see the light of day by anyone, it was a thought I had but after doing the math I realize it is impossible.
The slope of mount everest, as explained and found in this mildly annoying video:
http://www.youtube.com/watch?v=ECH7LQb75VU is found to be .76; a Tangent value of .76 translates to a degree slope of 37 (using the
http://web2.0calc.com/) Please feel free to disect and fix my mistakes in math, it has been a while
With 255 being the maximum altitude for block placement in minecraft, and 62 being the maximum height for sea level, (see
http://www.minecraftwiki.net/wiki/Altitude) we know that we have a 193 block space to work with. The height of everest is 8840m and base camps on the tibet and nepal sides are around 3200m. This means we have 5620m from base camp to the summit of everest. This is the area I think we should try to mimic as it is the most well documented area. Anyways with a slope of 36 degrees, and a height of 5620 we can find the slope to be 9388m long and the base to be around 7458m.
Taking this down to minecraft terms, by multiplying all values by around .035 we could bring it down to minecraft terms. The height become 196, the base becomes 261m which must be multiplied by 2 as i have done all calculations so far as a right triangle so it become 522m. This is a huge undertaking and it's late at night so I dont even want to begin trying to find the volume. Just doing this math I realize how silly this seems. I marked out 500m and let me tell you, it is a huge distance.