You probably weren't looking at an actual 120hz display, then. Yes, your display needs to natively be 120hz so you can see actual 120fps, not that smoothed out crap most TVs display.
And no, consoles cannot output native 120fps. Only PC can. (Most) TVs just smooth the motion to give the illusion of 60>fps.
I notice a difference between 60hz and 76hz. Smoother, and less screen tearing.
Vsync causes input lag, so uncapping your FPS does matter.
Was definitely a very nice PC with actual 120hz display. I could note a difference, but it was nothing substantial, and certainly wasnt blowing me away. If that kind of difference is important to ya, good on you, for me, it's gotten to a point where we're just splitting hairs. Like I also said, Splatoon at 720p and it's beautiful, frankly I couldn't care less if they could have instead got it to 1080p. At the end of the day, all those specs don't matter to me, all I truly care about is if itso a fun game that runs smoothly, and if it looks pretty, that's great too, but not a deal-breaker if it doesn't.