With the way a lot of the initial first wave of reviews is looking, Ryzen 7 isn't the answer for pure gaming. The 5 and 3 series aren't exactly out yet, so we average consumers know nothing about them other than speculation.
The hyperthreading of an i7 can help in some newer games, but on the whole, an i5 seems to be the "good enough" answer. Coming from a Sandy Bridge processor, probably just the IPC improvements alone will make quite a difference. A lot of older titles, or games built on older engines *cough*unreal3*cough* really like pure clock speed (and RAM speed for that matter) over core count, whereas games like BF1, GTA5, and WD2 lean more heavily on core/thread count. In essence, it depends on the games you like to play now, with some consideration for games you'll like to play in the future.
I guess I'll list examples of my own personal experiences to demonstrate what I mean. Planetside 2 (completely CPU-reliant, FPS doesn't change between my GTX1060 and my old HD4870) benefitted from a near doubling of FPS from an i5 4460 to an i7 4790k on the same graphical settings, and a little more than double with the 4790k at 4.7ghz, albeit not a completely stable overclock, at 2560x1600 resolution (<- does that have a name like 1440p or 1080p? 1600p?). Meanwhile, games like Warframe, heavily modded Skyrim (200+ mods including ENB), and Blade and Soul, gained 0-15%.
From what I've seen, 7700k can get really hot. Most reviewers had trouble keeping it cool without a 240mm+ CLC. It's the main reason I decided not to go for a full system overhaul and just threw a 4790k on my existing motherboard, with my existing cooler.
Is your PSU enough for it? You're cutting it close there, especially if you toss in an unlocked i7.