I picked up the 1700x on friday, here is my experience.
I have a 2500k@4.6ghz/2133mhzDDR3 and a 980Ti. I play at 1440p on a Acer 144hz IPS Gsynch Monitor.
I upgraded to the 1700x with a b350 Tomahawk motherboard and promptly overclocked it to 3900Mhz.
Gsynch used for all of the below settings.
BF1 at 1440p Ultra settings:
2500k = about 75-85fps in most areas in multiplayer
1700x = about 75-85 fps in most areas in multiplayer.
The games felt the same. My 2500k is smooth, no stuttering and such like some people try to tell you is going to happen on Intel platforms.
Dishonored 2: (Very High settings)
2500k = 1700x fps = 70-85 fps in most areas.
Both systems were essentially the same, didn't find 1700x to be more smooth or anything.
Fallout 4: (Ultra settings)
55-65fps in load areas, 75-85 in some outdoor areas.
2500k=1700x fps again
So basically, with my 980 Ti, the games all felt the same. I didn't really notice any difference subjectively. If I was to chart proper benchmark graphs, I am sure there would be a difference, but using MSI Afterburner and going off my "feel", they felt the same. BF1 ran smooth on both systems but so did Fallout 4 and Dishonored 2. I wanted to try ARK, but I had deleted it for space.
Obviously, I am GPU limited. So I couldn't see much difference in frame pushing power, but all the games I mentioned above run fine on Sandy Bridge.
The desktop and everything else felt better and smoother, not by much, but I was able to run more crap at the same time without any performance hit that you notice with the 2500k, so the 1700x is definitely a nice bump to multi-tasking. I was playing BF1 and had a video editor running in the background uploading a B350 Bios video and I recorded a bit more video with nVidia Shadow Play and it didn't hit me at all.... good luck doing that on the 2500k.
Overall, I am going to sell the 1700x (should only lose about $50 but whatever) and take the B350 Tomahawk motherboard back (nice little motherboard actually, if sparse), and then sell my 4 x 8 GB of 3000mhz GSkill Ram and I will wait until 2018 to upgrade, at which point I would get a Volta CPU, Ryzen Plus or a Coffee Lake 6 core. (Yes, I wasted a couple hundred in experiments).
I am on the fence about buying a 1080Ti. It seems I would get a 50-75% improvement in frame rates over my 980 Ti, and it would match perfectly with a new CPU next year, but I think for the games I am playing this year (BF1, the odd RPG that comes out, Mass Effect Andromeda next week, new Star Wars Battlefront later in the year if it doesn't suck) I am better off waiting until 2018 and getting an entire new build.
I honestly think that for GAMING, people are needlessly upgrading their CPU. Sandy Bridge and up are perfectly fine for this year IMO, provided you are willing to make a few concessions. Obviously, YOUR use may be different, so if you are streaming or doing productivity or whatever, you probably want to upgrade.
I think people are better off waiting for Ryzen Plus or Coffee Lake or perhaps Ice lake if it comes in late 2018. Cannon Lake is a laptop part obviously.
That being said, I think 1700x was a wonderful chip overall, I would have enjoyed seeing it paired to a 1080Ti and then comparing it, but I don't want to spend $1000 on a 1080Ti at the moment.