I think that getting you deck biased for new tapes as opposed to NOS is a no brainer. Most new tape is based on old formulations that have stood the test of time. The RMGI 911 has better headroom than any Maxell UD or other tape I used in the '70s. After what Paul stated in his reply to my post below I think I would go with 468 like he said. Why? Well, the last time I looked, I didn't see any Grammys on my mantle. Bottom line is, you're taking a chance with any old stock but with new tape, you can always return it if it's defective.
BTW I feel that it's important to support new tape manufacture. Sure, what we use is nothing compared to professionals, but every little bit helps when it's such a niche market ( what those guys must've gone through to secure loans to start production I can't even imagine).