Once the size: After measuring my calf circumference I would have used Size 3. But since I was not sure and I'm also a bit smaller, I ordered size 2 (II). Right Decision. They fit like a glove. They are very tight but if you made it first to put them (which is, incidentally, with the guidance process of tightening is much easier), they are super comfortable. They are at the base not too short and you also do not feel that something is squeezed.
Now to the effect: I regularly go running about an hour. It was also without the CEP stockings all right, but I was now running with the stockings and it was almost by itself. You feel lighter and also run it's easier. You do not get heavy legs and even my calf does not sealed after half an hour. I was able to walk with the stockings even half an hour longer. They are absolutely amazing and all the fun of running have, I can put these socks only to my heart. Invested in it and you will not regret it. Anyway, I'll order a couple of me, so that I can now wear always run at. Even my friend I convinced already and he will now also what buy :)