Well, I am almost ashamed that I have not tried any of my Schneiders fully open at 5.6 for the simple reason that everyone says/writes....."useless, mushy, no not really, only so-so, oh huge difference to f8, if you need 5.6 - buy Rodies".....and so on!
This has made me not even try it
Today I did for the first time. And what a surprise! The Schneider 35 XL at infinity and f5.6 gave me an incredibly sharp borderline of a castle about 150-170 metres away. Believe it or not, but at 100% view there was very very little that improved with f8. I am not even sure if I could pick out f5.6 instead of f8 in a test.
Now, my 35 XL has been to Schneider in Germany for recalibration and I suppose that has something to do with it as well. So, the tip of the day, if you have a 35 XL and it is 'mushy' at f5.6 - get it recalibrated!
I could not be happier, it is not only usable at f5.6, it is darn sharp and impressive