Yeah, 8GB of RAM should be good. A quick look through my Steam library shows that most games seem to recommend 4GB of RAM. Watch Dogs is the first game I have seen list 6GB of RAM on the system requirements. I'm sure there are exceptions but I haven't seen that in listings before. Having 8GB is good for a little bit of future proofing. People with ridiculous rigs with 32GB of RAM are just throwing money away because no games need that much.
I don't have DayZ but the system you listed should be able to play it at 1080p with high settings. It's an open environment but it doesn't look like the most graphically intensive game. I think it will do a nice job with modern games and you will rarely have to turn many of the settings down if you are playing on a TV.
I know DayZ doesn't look like the most graphic intensive game but from everything I've read it sounds like it demands quite a bit from a PC. Maybe it has more to do with multiple people on a server or something. I know that people's frame rates really drop when they are in some of the cities where there may be more people playing and zombies roaming about.
I know what you're saying about the wasting of money. I've seen videos of people putting together these $3,000 rigs and adding high end hardware just because they can. It's like computer geeks are no different than car buffs, always showing off their ride.