A large music retailer told me that the Series III tenor neck along with the Super Action 80 and SA80 II sax is the hot combo. I am using III necks on my MK VI and Selmer USA tenors. The USA came with a SA80 II-type neck. I would bet that if you try a III neck you will like it, but you should also have your SA80 neck repaired - its good to have choices. Whatever you try, use a tuner when you play it. You can get a good free tuner app for your phone which is what I use, and its very handy for gigs or anything else, because its always in your pocket.
The Series III Jubilee necks now being produced are great and they come in all materials/finishes. I use a Sterling one on the USA and a brass lacquer on the VI. I can interchange them if I want or use the original VI neck on the VI, but really the III neck is better. And, I just had that original neck checked out and tuned up. It is better, but no match.
I saw a used III Sterling silver early Jubilee tenor neck on FB for $350. If I didn't already have one I would have jumped on that. This neck is unbelievable but also a little 'flexy' so you have to be careful with it.