Interesting. Don you think af speed is similar on both?
The only differences that are noticeable between the two lenses are the slightly shorter Fov on the 50 and build quality. The 55 is a bit bigger, a bit heavier, and feels more solid. The 55's AF does feel a bit smoother. Whether or not it's any faster than the 50 is difficult to say. The 50's AF is quite fast and I've had no probs at all with it. I used it skiing all last winter and it nailed everything. As I mentioned above, IQ wise....no discernible differences on the a6500...or at least not enough to warrant the extra $. In the hand the 55 feels like a higher quality lens, as it should. But I can't tell much difference when it comes to AF speed and end result. Remember....we are talking about the inexpensive E 50/1.8 (~200 on the used market). I get the feeling many people are not familiar with this lens cause it is APS-c only.
Here's a link to a simple mid afternoon portrait taken with the lens.