I have found and read one review of the Silverstone and it didn't get a good score (very bad ripple suppression). And after I asked the question, I have read some reviews of Cougar in german. I couldn't find english reviews because it is new (released in late July).
So, for the time being, I am choosing Cougar psu since it's newer, cheaper and in stock (I have to wait for the strider and I can't get a confirmation for the estimated time of restocking).