I play games on a core 2 duo system and I have friends that have got themselves I7, I5 and I3 systems and I also have my brother that play games with us on his laptop running an I5 and integrated graphics, he has the hardest time and cannot always play. we all play over team speak and tend to play the same games together. we don't play browser games.
what I have noticed over the 2 years that my friends have played with there core "I" PCs is that my core 2 duo can do the same things as there processors. but of course there is the occasion that my core 2 duo dose show its age from time to time, what I am talking about is in some games if I Alt+Tab it can hang a bit, but I don't find this a big problem by the fact that I only spent $26 NZD.
in short the core 2 duo can depending on the one you get can do the same things as modern processors. I would still probably get a core 2 quad just because it actually can out do some I5s. but the core 2 duo is awesome as far as price to performance goes.
the I3 is not a chip that I have personally own or have used so I cant tell you what its like to use but I can tell you how it performs because I have benchmarked it against my core 2 duo and my other friends I7 and I5. from my experience the I3 is actually in practice just as powerful as the I7 (I understand that there are more than one C2D, I3, I5 and I7) both the I5 and I7 systems have a GTX 960 Ti SC I even went to there houses and checked this the Mobos are different and really everything else but even though this the I3 did just as well as the I7, and was not a bottle neck at all the I5 is on a standard HP OEM pc (so is my core 2 duo) but the I5 even though its running a GTX 780 Ti it still does just as well, the fps differences are so small that its hard to even see when looking at the fps counter and reading it.
all that I am going to say from here is that I think "hardcore gamers" are going over the top in a lot of the situations needing 80 GB ram and an I7 over clocked to 9.5Ghz and a liquid nitrogen cooler to run it and 50 TB to store there games, it is just them wanting the best possible system even if they don't need it. and then the best is that they tell everyone that they need that over the top system as a minimum standard, and that a core 2 quad is not good enough for people that want to play GTA V because it dose not make 967 FPS, and that they need gaming keyboards and mice. don't get me wrong there is a place for that, but if you look away from the "best system out there" to something like a core 2 quad for a minute and see what it can do it makes you realize that it dose not tend to matter all that much about the latest and that there might be an older CPU, GPU, RAM chip that dose the same for you even though its older. I don't honestly at least for what I do see a difference.
we play things like War Thunder, GTA V, Heroes & Generals, Payday 2, and other games but I cant be bothered to list them all right now.
hope this helps even though I am a few years late.