120hz monitors and some basic questions about performance

Hi. I need a new gaming monitor. I've been using a Viewsonic 19" CRT for many years but now it's dead. Performance is very important for me, at least with first person shooters. I used to play them at 100 fps, 100 hz, with vsync. I know about looking for 2ms maximum, minimum input lag (don't know where to find that information), etc. What I don't know if I should buy a 60hz monitor or go for a 120hz model, quite more expensive. Let me make clear that I am not interested in 3D displays with the glasses. My doubts are:

- Are these monitors better displaying moving elements, even when you are using a game locked at 60 fps with vsync. I have a 120hz TV and it has some kind of technology that makes that the motion is like more fluid and natural. Maybe the 120hz technology in PC monitors makes the same? For instance, with a XBOX360 game using HDMI (the monitors cannot be set 10 120hz with that connection), will a 60fps game in motion look better, the same or worse?

- I understand that setting these monitors to 120hz will make a game that runs at 120hz move almost as perfect as with a CRT. However, do you need vsync for that? What happens if you computer is not able to keep that framerate in the game? In my CRT, when set to 100hz and with vsync, if my first person shooter falls to 90 or 80, the stuttering is quite noticiable. It that is the same with 120hz TFTs, it would be useless if most of your games only reach 90 or 100 fps, because you would have to, either disable vsync (you get tearing), or set the monitor to 60 hz or 70 hz, so that the game is locked at that framerate and runs smooth, in which case there wouldn't be any difference with respect a standar 60hz monitor, or would it be?

- If the problem I have commented before really happens, would it be posible to set the monitor to 100 hz, for instance, and therefore run the games with vsync. Actually, with my old CRT, I prefer to use 100 hz, instead or 120 because my Unreal Tournament III, for instance, manages to stay at 100 fps most of the time, but not 120.