Hi Doug,
thanks for your kind review.
I got my vintage Ampex from a guy on Ebay. There are reliable sellers and
there are goons who are only too happy to try to sell sticky-shed tape,
so I made sure the few reels I purchased are from 1995, still sealed,
in the newly (then) designed box with the date code on it. It is as good
as gold. 
Apart from RMGI tape, I also have some NOS Quantegy 406 and only last
night I ordered some more ATR media, which I’ve yet to try. By all reports
it is as good as if not superior to 456. However, I have to say that the
RMGI tape has performed brilliantly for me and I have no issues with it.
It is true to say, though, that each tape has its own characteristics but
so far I’m well impressed with the old 456. 
I no longer offer the layback mastering service. No one was interested,
so I took the hint.
Cheers,
Jet