My following comments are purely a guess based on my experiences with B&W D2 and D3 speakers.
The older 805S will likely be much more refined than S3 in a lot of ways. However, a couple of things to keep in mind. The older generations used the woven kevlar midranges and midwoofers. These had a nasty breakup problem in the upper midrange. It sort of had its own unique texture, but it could also come across as somewhat of a distortion in the upper midrange or ringing. Also the older tweeters were aluminum dome and have been described as sounding bright due to the metal dome breakup.
The newer S3 models have evolved with newer and better technologies to counter these old behaviors. However, S3 is likely not going to be as refined as the 805S level and would sound "low fidelity" in comparison.
The older 805S will likely be much more refined than S3 in a lot of ways. However, a couple of things to keep in mind. The older generations used the woven kevlar midranges and midwoofers. These had a nasty breakup problem in the upper midrange. It sort of had its own unique texture, but it could also come across as somewhat of a distortion in the upper midrange or ringing. Also the older tweeters were aluminum dome and have been described as sounding bright due to the metal dome breakup.
The newer S3 models have evolved with newer and better technologies to counter these old behaviors. However, S3 is likely not going to be as refined as the 805S level and would sound "low fidelity" in comparison.