Okay I know this is totally not a Chevy question but lets treat it as such.
I have a Mazda Millenia S from my parents to put the 66 Impala on project status. The Mazda needs a timing belt change. Just think of it as a blower belt because well. It's on a blower and it keeps the engine in time. SO.

The question is what should I look for in a belt? I see that some belts are described as "Highly Saturated Nitrile". And some are just OE replacement.

Can anyone tell me the difference?

I want super-durability so I don't have to do this again for a very long time.