I still use the 4790k and see absolutely no reason to upgrade yet
Don't listen to the reviews! Although the 8700K is a very expensive upgrade it most certainly does improve over the 4790K. I have a 4790K here with a 1070 in it and it is running a 3.5K monitor. It can not maintain 60fps at all times. A PC that is exactly the same except it has an 8700K in it doesn't suffer from the same FPS drops that the 4790K does. Of course it depends on the game, and settings and so on, but I was actually very surprised at the difference. The 1070 actually runs a few degrees hotter in the 8700K because it's managing to maintain a constant fps. Amazing. Listening to reviews I had hardly expected any difference at all, but there certainly is. Getting back to the 7700K, the difference isn't that vast for games, but the 8700K is definitely better and after my own experience with the 4790K and 8700K, I would be reluctant to believe everything you read in reviews! The 8700K is not that much more expensive and I would go for it every time.