I've never had any problems with the AF speed of the 55 or 80 on 50S II. It's the pointless hunting back and forth every time you want to view an image on the screen that is extremely annoying. It doesn't add anything at all. Just bad software that has nothing with AF to do.
BTW, I also find the 55 very, very difficult to focus manually. Not only does it "jump" in too large increments; the focusing ring is more or less the whole barrel and it's almost impossible not to twist it and bump focus when tripping the shutter. No damping of the ring what so ever.
