Data point from the '89 Schwinn catalog; it looks like the the Tempo was one step above the Prelude. The Circuit was one step above the Tempo. There were three models with aluminimum frames(974, 754, 564). It's a little difficult to judge where they fit in the lineup as there are no prices in the catalog. At the top of the line were the Paramount and Prologue. These models look like they may have been sold as framesets only. If you can identify the year of the bike when you get it(look for four digit number stamped into headbadge) I may have the catalog for that year and can tell you more about it.