Will high end speakers on high end amps all pretty much start to congest at these 100-105 DB ranges?
At 2 meters from the speaker - yes absolutely. Soundstage will not even test speakers at 100 db SPL as most would get damaged - see quote below from soundstage:
As volume increases, all frequencies should rise at the same rate. However, as a speaker is stressed, compression will occur at certain frequencies. The stress may be mechanical, thermal or otherwise. This test shows those frequencies at which deviation occurs as a result of compression. Many speakers show slight deviations at 90dB. Most speakers start to show serious deviations at 95dB. Very few speakers can be tested at 100dB without damage.
Furthermore remember that soundstage are NOT making IMD tests - so their results look artificially good (when a speaker plays simultaneously high and low frequencies you get MORE distortion).