Global is tuning for all games but you can also have individual tuning profiles for games. If you set up a different overclock in a game profile it will show up there when you click the global tuning drop-down menu.
No, he is not asking for what "Global Tunning" itself does, but the sub option. System Control That's the CPU OC feature for when you have a 6000 GPU + 5000 CPU. It will OC both, the CPU and GPU. Why it's shown to you with a 5700XT is beyond me. They might have silently enabled it with the latest drivers in older cards.
Yes, this is what I am talking about. I've updated the title to also reflect this. I never noticed this additional option before and didn't know what it does. It's a little confusing to me because I already have CPU and GPU. And last I check that was all that was found in Global Tuning. Now I see the addition of System? And didn't know what it suppose to do in addition to what CPU and GPU already does. From what you've provided it OC's both CPU and GPU. But when I set it to custom I would think I would see additional options but I do not.