I have both the 40S and 50S. I don't see any difference in quality of the image. The 50S uses 67mm filters like all my other S lenses. The pro hood fits the 50S. But, I like and use the 40S more. Downside, takes a 95mm filter, which I have none of. I found I can use a Cokin P filter. They fit just inside of the scalloped hood and I hold them on with a rubber band looped around opposing corners. I would prefer a high quality glass filter but cannot afford the price of a set of 95mm, even if I could find them.
The extra few degrees are useful and so is the extra depth of field of the 40.