Alright, I admit it's been quite a while since I was in the market for anything like this, so...the last monitors I bought were 27" 1920x1080 screens and they were pretty much the top of the heap, if that tells you when that was...

I'm trying to figure out what kind of screen I want to use as a monitor for the "gaming" computer I'm going to put in the living room. Kat really wants a computer at home again to game on, (she has a Surface Pro 3 for school stuff), and got the OK from the Mrs. to bring one of the rigs home (I have all 5 of the 3930K rigs at the office right now).

How much of a graphics card does it take to run a moderately demanding game at 4K these days? - like the latest Tomb Raider or Counter Strike CS:GO are a couple that Kat likes to play.

Is there much of a difference in what you see on the screen at 4K vs 1920x1080 screens? I've honestly never used or even seen a 4K screen, I don't think.

Is there any reason I couldn't just use a medium size - like thinking anywhere from 35 - 45"? 4K LCD TV screen for this? Might be kind of nice in the living room, just thinking out loud there...or should I just go get another 27" 1920x1080 screen for a pittance these days and call it good? Can't believe how low the prices are on them compared to when I bought the couple I have at the office right now. But then, makes me wonder just how much better a big - 32" plus - 4K screen might be?
Thanks for any thoughts on this!