I'm sorry, I call bullshit.
Mescaline could be comparable to MDMA (please don't use fake acronym XTC... it's retarded)
because of their chemical similarities (they are both phenethylamines).
However, I don't see how the mescaline from Peruvian Torch is different from the EXACT SAME MOLECULE in San Pedro or Peyote. Unless there are other psychoactive alkaloids in the plants, which I have never heard of, the effects should be the same.
Potency may vary which could explain a difference in strength. Presence of other components (such as tannins, for example) could either slow down or accelerate the absorbtion of mescaline, which would explain differences in the length of the trip and again the strength.
Example: One could say that coffee and tea offer rather different experiences. Tea being a lot mellower. This has been studied: they both contain caffeine as their active stimulant but the tannins in the tea slow down the absorbtion, stretching out the effect of caffeine on a longer period. Kind of like snorting vs. IVing. Also coffee has bowel irritation as a side-effect, which makes the experience different i'll agree, but not in a "differently psychoactive" way.
If you consider side-effects (digestion troubles, dry-mouth, etc...) to play a role in the overall experience then yes it can be different. But I believe that ultimately mescaline is mescaline and will offer the same effects from a qualitative point of view.
Psychedelics are so much influenced by mood set and setting that you will never be able to produce the exact same effects twice.