W&S boxlocks of approx 1900 to 1970 are all good workaday guns but like any gun may have suffered from use and abuse over the years.
I don't consider them very good value as they tend to attract prices in the UK out all proportion to their quality. The reason for this is that the marque is well known and everyone knows someone with one or had one once.
Internally they are okay but very much in the mould of the AYA No 4 which is essentially a copy of the W&S. For the money, I would tend towards the latter as the parts are readily available (albeit they need hand fitting) which is more than can be said for a W&S.
If you are wanting an English gun, then I would tend towards the lesser known Birmingham makers, you'll probably get more gun for your buck.
As to 20g's, relatively few were made which will push the price much higher than a 12 regardless of who made it. Furthermore, they were traditionally bought for youngsters and ladies and nearly always have been severely shortened. Fine if you are 5' 2" in your socks, a bit of a problem if you are a 6' ape!
For myself, I would go for a 6lb 12g and shoot 3/4-7/8oz loads in it.
