I was not aware that there was such a thing as a T-Y gold disc.
Honestly, I think this is a moot point to begin with for the following reasons:
Even with the best media, if you are doing serious archiving then you are going to want to make multiple copies on different brands of media. Even the best brands / types can be hit by bad batches.
If you are thinking of keeping you media around long enough for gold/pthalocyanine to make a difference, you'll also be pushing into a time when DVDR will become very mature and also viable for long term storage. Therefore it will make sense to re-archive to DVDR anyway.
So if I was you, I'd get two types of very good CD-R discs (say, Prodisc and TY silver) and burn all my archives twice.
And then in 5-10 years, I'd just recopy those to DVDR.
Repeat the same with BD-R in another 5-10 years.