The SCSW, p. 268, writes 657s were introduced in 1986 with three barrel lengths, 4”, 6”, and 8 3/8”, and that while the 4” was discontinued in 1988, the 8 3/8” wasn’t discontinued until 1993. There have also been batches of 8 3/8” PC 657s.

It appears to me that newer members to the handgun shooting sports don’t appreciate how may long toms were built during the roughly 10 years that long range silhouette was popular. IMO, due to its short production life, increased interest in carrying concealed and short range draw and fire fast matches replacing long range matches, the 4” 657 is the barrel length most likely to fetch a high price.