I'm hardly an expert either, but if they are so different, then why is X regularly cut with Meth, Caffeine, Cocaine and other amphetamines? The dealers are pretty good at coming up with cuts that are cheap but give a similar high.
You might find this interesting:
http://blogs.dallasobserver.com/unfairpark/2012/03/dont_panic_but_theres_probably.php
Dallas used to have a bunch of Acid/Ecstacy attitude bars. They were pretty funny because there was no dancing, but they blasted house music. The music was so loud that you would have to txt each other from across the table to have a conversation. Most people just sat at the tables, looked around, and occasionally nodded to each other, with pupils dilated the size of dinner plates. endtangent/
Anyway, it's pretty interesting what this chemist is saying about the supposed "Ecstacy" that comes into his lab.