If speed and performance = desirability, then I'd say late-'80s, particularly 1989 Schwinn is the golden year. Paramounts were golden, as always. This would be the final year of the epic three-year-sub-Paramount reign of the Tange Prestige-tubed Prolouge. Klein-like (design partner, right?) Schwinn aluminum frames (that font!!). Legacy-of-the-Peloton-lives-on with the Columbus SL-tubed Circuit. The Tenax-tubed Tempo finally got a 27.2mm seat post spec, so the tubing was certainly better than before. Captain America paint job for the Prelude. Everything else benefited from late-'80s index shifting from Shimano and (to a much smaller degree) Suntour. Geometry on these upper end Schwinns was very good and very proven, and nearly similar spec was spread across numerous models.

My experience is with a number of aforementioned examples. And below is my '87 Prologue, essentially the same as an '89 save for the year of manufacture. This is a bike you will never be disappointed in.