From time to time I see claims of one or more species of Amanita mushrooms containing bufotenine and/or 5-MeO-DMT. These claims are made both about the lethal and the entheogenic species.

What truth is it actually to these claims? And if they do contain bufotenine or 5-MeO-DMT, then how large quantities are we talking about? Enough to really affect the trip?

No.

"Bufotenine is also found in several species of Amanita mushrooms, including Amanita muscaria(disputed), Amanita citrina, and Amanita porphyria."
-Wikipedia

There was a chemical analysis of different amanita muscaria extract products which contained low or no amounts of muscimol and ibotenic acid but were found to contain 5-meo-dmt, 5-meo-dipt, harmalines, atropine and scopolamine. Maybe this is why some people think they contain 5-meo-dmt?

5-meo-DiPT is naturally occuring in fungi?..

Those extracts must have been 'pimped'. I don't believe that amanita muscaria contains all those substances.

This rumour about amanita containing DMT or 5-MeO-DMT started somewhere when (i believe) shulgin mentioned, without having tried the mushrooms himself, that they COULD contain 'x' based on how powerfull it's effects apparently can be if taken enough of it.

As far as i know this has never been proven AND i've never heard of anyone having had experiences with amanita that even came a bit close to those you have with tryptamines.

Based on my own experiences with it, i would also say that it doesn't contain any of the mentioned substances, except from 5-MeO-DiPT, with wich i have no experience.
You may expect 5-MeO-DiPT to have some simmilarities with the more familiar tryptamines though, i suppose.

Yes, that's what I mean. I forgot to add that none of that was found in verified A. muscaria and pantherina plant material.