NAKAMICHI: What R to R is better than Nakamichi Deck?

I have some 3 head Nakamichis from the early 90's and so far none of the old reel to reel decks can beat or even match them for freq response and S/N especially with metal tape.

How much would one needs to spend to get better results?
Any Akai or Teac Pioneer or Sony machines?

I'm not in the market for Studer or Revox machines right now.

Thanks