I've used S-23 a couple of times with good results. The first time, after reading reports of excess fruitiness with cold ferm temps, I went in the mid-50s for a Bohemian pils. Turned out well, won a few medals. The next time, I wanted to see if it really was fruity when fermented cold; did virtually the exact same recipe, fermented at 48, beer turned out very well, although it was struggling to finish by the time I warmed it up for a d-rest. No fruitiness, the beer won some medals, including a gold a few weeks back.
So it will be just fine at 50 or even below, but make sure you pitch LOTS (200-300 grams rehydrated per hectolitre of wort) and keep an eye out for when fermentation begins to slow down. In a nutshell, it will work, and you can expect a nice beer to result if you take care of your yeast.