I have sailed an extended version of Stevens 50 and she was one of two most comfortable monohull
boats I have ever been on. I absolutely loved how she moved. She was easy to drive and kept good speed thru somewhat turbulent conditions of that day.
were all fine quality materials (boat built, I believe, in Taiwan). She was a bit demanding on maintenance
though - teak deck
and plenty of varnished trim above deck
If S40 is from the same stable, I would definitely go for a test ride followed by a survey
Good luck, tell us how it went!