It's difficult to say exactly how the 2070 will perform, but since the 2080 only performs comparable to a 1080 Ti, the 2070 will likely only perform comparable to a 1080. And since they'll be asking around $600 for the 2070 at launch, that makes it kind of a hard sell, considering there are 1080s available for $450-$500, and some 1080 Tis for as little as $650. And consider that a 1080 would only get you around 20% higher frame rates at best compared to what you already have, assuming your CPU didn't hold it back. At 1080p, your CPU would most likely be the limiting factor in many games, and in some, you might not see much higher frame rates than what you are getting now.
The 20 series also offers some visual enhancement features like hardware support for raytracing effects and DLSS antialiasing, but they require explicit support in games, and as of now, no games support either feature so it's difficult to say how they will perform on the 2070, or if those effects will even be widely supported in the near future. I suspect that it would probably be better to wait some months to see how those things pan out before considering one of the 20-series graphics cards.
As for a CPU upgrade, your CPU is still fairly good, though an 8700K would offer higher performance. Again, that won't necessarily translate to significantly higher frame rates if your graphics card is holding it back though, which a 1070 would in many games. And of course, you would also need a new motherboard and new RAM to go with the CPU, along with a capable cooler if you happen to be just using something like an Intel stock cooler now, as that would not likely be adequate. Also, note that Intel should soon be launching 9000-series CPUs that will likely be slightly faster at gaming than the 8700K, probably within the next month or so.