Both sides have their advantages to be able to get the most out of your 4k tv, I could see you happy with either one.
What it comes down to is games, games, games. Seeing that you probably already have a good library of games on the PC, getting the 1070 will allow you to play them with better graphics, although I would still invest on a better CPU if you want to get those really high ultra settings on some games. So chances are that you could go nicely with a cheaper vid card if you plan to play most the same games and just want to see them look prettier.
I would agree that PC does have the best prices for games (steam, humble bundles, even certain sites will give their games out for free as a promo every once in awhile). Although I wouldn't neglect that you can and probably will find that Playstation gamers have good access to cheap games and free games every month. PSN plus will reward you with enough games to fill your time every month and PSN usually has decent sales going on almost always. subscribe yourself to cheapassgamer on twitter and you will see that there's enough deals going on a lot. Not to mention gamestop, best buy and other retailer deals. I have found that most games drop price really quick anyways, so you have a good chance of getting the game you want sooner or later.
On the side of getting a PS4 over the 1070, its all about those exclusives. I'm a PC and PS4 gamer, primarily for those exclusives. I can get those Xbox games sooner or later on PC or PS4. but PS4 first/second party exclusives are a must for owning a PS4. You can even get your hands on some of those exclusives you missed out on with PS3 via remasters or rereleases. Sure you can also now subscribe to PSNow on PC and enjoy them if they become available on that network.
The only argument against getting a PS4 Pro would have been if you already had a PS4 and were only upgrading or if you by chance were willing to wait and see if maybe in a year or two, they'll announce a PS5. Sony seems to be on a wait and see how Xbox scorpio does before thinking ahead kind of moment.
To wrap it up, think of the games you WANT to play and are interested in that will be coming out for the next 2-3 years. Thats where I would put my money. My personal choice if I had your current rig, would be PS4 or PS4 pro. mostly for the games. I find that most the games I like on PC would probably run ok if I had your current rig and if not then I can enjoy them on PS4.