i5 6600 (no k) not enough for open world cpu intensive game like Witcher III and Assassin's Creed: Unity?

Assassin's Creed: Unity is an old game tho.. Premiered in November 2014. But I heard it is a failure in pc optimization. But in that youtube video it can reach 65+fps with an i7 6700 (no k) processor. A Tom's Hardware Moderator also said that I shouldn't trust Youtube that much and I heard that i5 6600 is a great processor to be paired with GTX 1070 and won't bottleneck the GPU. Some of my friends even said that even if I upgrade to i7 6700 it'd be a waste because I'll probably only gain around 4-5fps. Some said it'll only increase the performance by 5%. So I doubt whether there's another factor that could cause the low fps? RAM usage is ok I guess. This game uses around 4GB of my 8GB RAM. Or probably because my system is still DDR3 not DDR4? Sorry Noob in PC building. This is my first build.

Quoted from Tom's Hardware Moderator synphul:
"In past benchmarks the i7's performed slightly better in witcher 3 than the i5's. Hyper threading helped maintain higher minimum fps and improved frame times a bit. If it's worth a 50% price increase for 5% or so performance then sure. Nothing wrong with going with an i7 for sure.

It's not all open world games, it really depends on the game. Witcher 3 specifically showed a bit of improvement with a hyper threaded i7 over an i5. The i5 did quite a bit better than the i3, even though they both process 4 threads at a time the i5 has 4 actual cores which gives it the advantage over the i3. In a similar but less significant way the i7's ht imrpoves performance a bit.

I find youtube vids hard to verify, everyone seems to be getting different results with different hardware a lot of the time. Not saying they're totally fake but a lot of variables. Even the older 4690 i5's were capable of pushing around 60fps and only dipping into the 50's at times, I can't imagine the 6600 doing worse.

I'm also not sure how things are running with ddr3 and a skylake cpu. Ddr3 typically runs at 1.5v, ddr4 runs at 1.2v and ddr3L (low power ddr3) runs at 1.35v. Skylake according to intel should run on ddr4 or ddr3L (which is already .15v higher than ddr4). Your ddr3 is .15v higher than that. The memory controller is on the cpu itself and pushing ram faster with higher voltage is typically considered an overclock. Having a locked cpu I'm not sure how that plays out. Maybe there is a bit more stuttering or something going on because of the ram/cpu combo there. You may want to ask in the forums since I'm not sure how that effects the memory if at all, if it undervolts and therefor slows the ram down some? I can't really say.

Some people say it's fine, personally I choose to believe intel's warnings against it. If nothing else than for the reason they go out of their way to say ddr4/ddr3L when they openly offer overclocking oriented components like the k series chips. There must be a reason why and even an xmp profile with ddr4 isn't going to increase the voltage through the memory controller like running out of spec ddr3 ram. In the past there were boards that supported 2 types of memory but it was moving forward so the newer ram it also supported was lower voltage than the ram the platform was built around. Not going backwards to support higher voltage ram through a memory controller designed for a specific platform."

I've tested it in game debate as well but when I look at MSI Afterburner this game only use 4,5GB of my RAM max. Never go more than that. What is your opinion in this? Oh and GTA V took 7.5GB of my RAM but still run at 60+fps smoothly.

yes I could see it from MSI Afterburner in game monitoring that all four cores stay at 100% all the time sometimes drop to 98% tho but only for a while and this is a new Windows 10 installed it a month ago and I have never opened untrusted sites on this pc (should be clean). Power plan is set to High not power saver or balanced. Thank you for your answer anyways!

it is sitting at 65C max. And I used intel stock cooler.