Wecome to the forum Jonesie.
You' opening a can of worms with Mitsui, as the company (MAM) has splitted into two companies (MAM-A and MAM-E), producing media of rather different quality. Now lots of us, here, are very skeptical with anything MAM.
Things aren't clear, at least to me, as which Mitsui media can be considered as good or not. But I think that Dakhaas and Dolphinius Rex are quite knowledgable when it comes to the whole MAM topic.
"Archival" quality, and use of gold in the reflective layer, can be total marketing bull**it, as the manufacturing quality is just as important as the material used. Don't buy into hype without having consulted tests from reliable sources.
I don't know how you tried to search the forum, but I found lots of posts related to Mitsui gold media:
Can't help you further.