A full Reynolds 531 frame is mainly a matter of prestige. In practicality, it is not so important, as stays and forks are a compromise in design. In these applications Reynolds 531's potential weight savings cannot be fully realized because the forks and rear triangle would be too whippy. Stiffness in a round tube is a function of the material’s modulus of elasticity, its outer diameter and its thickness. All steels have a similar modulus of elastic and the stiffness primarily becomes a function of diameter and thickness.

A main triangle can maintain good stiffness, primarily due to the larger diameter tubes. But shrink the diameter, as in the stays and fork blades and things start to get whippy. Reynolds 531 seat stays in the 1970s were relatively thick, at 0.9mm. While there is not a lot of reference material available for hi-tensile seat stays, those offered by Tange were 1.0mm,. So, assuming other manufacturers were comparable, even if the seat stays were hi-tensile steel, you're paying a very small weight penalty, only around 30-40g. This is why designers often substitute lesser grade material in the stays and forks. It saves money without affecting the weight very much.