Hi, thanks for the replies !
Interesting to say, that two hours ago the website did cause high cpu, and now it does not.
It did that even with minimized Opera. But I think, Opera got a small update meanwhile - it is now 50.0.2762.58, and maybe it was a lower number after the comma before.
The snapshot I saved does take an unusal long time to load, about 15 seconds, which is considerably longer than loading it online . But after loading, CPU goes down to normal.
I'm on Win10/64 with an i7-6820HQ w 16GB RAM/512GB NVME SSD, DSL 20, no Java installed, but of course some other things like Flash. I have set up this machine recently, and the possibility of PUPs is rather low. But there are no gaming clients, nor any Skype or similiar clients. I tend to have a slim system, because I need most of its power for music production, where heavy background process can cause audio problems.
However, On Win10, it's not so easy anymore to 'know your tasks', since MS intruduced a lot of new processes and services. They even change service names and structures sometimes to hinder people on disabling them - best example is the user experience, which is clearly very important to the company.
So for the problem, it seems to be gone for now. Wether it was caused by an AD, a script on the site, or an intruder who read my CPU cache via a hidden Ad script, or simply an element in the ads that was hard to render, we won't know.