1 For me the difference is visible enough to warrant a €100- extra. But I own a 4k screen. Some games defenitely run better/more stable on pro hardware.
2. Its getting more common that you can choose your settings but I would not say a majority. Ni-oh and God of war did though.
3. On some games during intense moments it can be, but usually its pretty quiet.

Please excuse my (probally) poor grammar