I got this mail last week:

Hi Joel,

Quick question, I can’t decide between the Summilux SL 50 and the Summicron SL 50.
Price is much the same, and I can handle the bulk of the Summilux – but my  hesitation is based on the slower focus speed of the Summilux. Understandable as it is a bigger lens, but in practice have you found this any issue at all?

Many thanks,

It’s Joeri, not Joel, but you’re forgiven for that. If the slower focus speed of the Lux is your only concern, than I’d say, get the Lux. I haven’t worked with the 50 Cron, but I have used the 50 Lux on a couple of weddings. If I can make it work on a wedding, it’s good enough. What I found is that the 50 Lux seems slower than it actually is. While shooting I often got the impression it didn’t really focus quick enough to nail a shot, however when I reviewed my images, it turned out to be pretty perfect. There were only a handful images out of focus (out of at least 1500 shots).

You might also consider the Panasonic 50/1.4, or even the Sigma…