Drownzsurf :
I didn't want to sound like a smartass, so, I apologize if I sounded that way.
No, he's referring to me, though I find it hilarious he can't even call me by name.
Rcarlin, the first thing you miss in calling the 870 the "greatest bargain right now" is that it doesn't apply to anyone with a machine newer than 2009. And really, if someone has a machine from about 2007 and on, they probably want a more substantial upgrade, as well.
You haven't listed anything mind blowing or what I and others haven't said for a while. No, overall CPU per-core performance hasn't moved a lot in the last few years. What you fail to notice is that you're getting slightly more performance for significantly less power and heat. That's been the R&D direction lately as mobile and integrated device use has surged. I know some elitists complain about it, but I haven't been hurting for CPU power since I was finally able to upgrade my ancient XP machine back in 2011.
That example of the Witcher 3 likewise only affirms that a good GPU is king in gaming, also something that most of us have known for a long time. And the difference between an 860 and 870 is only 133 MHz, hardly noteworthy. As for whether the 870 will "bottleneck" a GPU, it's more accurate to say how much it bottlenecks. Every CPU has some kind of limit, especially when talking about top-shelf graphics. Don't believe me,
check some benchmarks. What matters is if your CPU ( or GPU as the case may be ) actually limits your performance so it's below the level you expect.
Tech sites and reviewers have been saying the same thing about Sandy Bridge, Ivy Bridge, Haswell, and Devil's Canyon: it's a nice step up, but it doesn't offer such huge performance over Nehalem that upgrading for the CPU alone would be worth it. If you're coming from an older setup, like Core 2 Duo or earlier, then you'll see marked improvements. A big reason a person would want to upgrade from LGA1156 is for the new auxiliary features like better RAM and SATA controllers, M.2 slots, USB 3 and 3.1, PCIe 3.0, etc.
Biggest of all, I would never recommend someone get used parts for a whole system rebuild. It's incredibly easy to abuse CPUs and motherboards without showing any external damage to them, so you rarely have a visual indicator of whether it's about to die or not. They can be overclocked too aggressively, run too hot, and have any number of other problems. You get no warranty, no customer support, and possibly no future driver support. Unless you know who it's coming from and how they took care of it, or can get some kind of service agreement from an authorized refurbisher, I'd never buy used parts for a build.