i5 6400 + gtx 1070 vs i5 7400 + 1060?

Solution
I agree a better solution may make sense for the budget, so if you want to discuss that perhaps give a BUDGET for the case + internals (including Windows) and we can make a PCPARTPICKER suggestion. Possibly Ryzen with the 6-core R5-1600 CPU.

As for the question the answer is the GTX1070 build.

More specifically:

1) i5-7400 is about 7% faster than the i5-6400
- thus that's roughly about the MOST you can expect for FPS improvement if there's a severe CPU bottleneck. It may be closer to 3% or less.

2) GTX1070 vs GTX1060 6GB (not 1060 3GB)
- closer to a 40% advantage in FPS or just better visuals, or combo of better visuals/FPS

https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1060/26.html

OTHER:
PUBG seems to be mentioned a lot...
I agree a better solution may make sense for the budget, so if you want to discuss that perhaps give a BUDGET for the case + internals (including Windows) and we can make a PCPARTPICKER suggestion. Possibly Ryzen with the 6-core R5-1600 CPU.

As for the question the answer is the GTX1070 build.

More specifically:

1) i5-7400 is about 7% faster than the i5-6400
- thus that's roughly about the MOST you can expect for FPS improvement if there's a severe CPU bottleneck. It may be closer to 3% or less.

2) GTX1070 vs GTX1060 6GB (not 1060 3GB)
- closer to a 40% advantage in FPS or just better visuals, or combo of better visuals/FPS

https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1060/26.html

OTHER:
PUBG seems to be mentioned a lot, though I'm not sure if it's very well optimized yet. In particular for PUBG:
http://www.tweaktown.com/articles/8189/playerunknowns-battlegrounds-benchmarked-cpu-gpu-war/index3.html

"Battlegrounds loves CPU frequency over CPU cores, so the 4C/4T processor at up to 4.2GHz screams in PUBG, while the 6C/12T processor with Ryzen 5 1600X clocks in at 4GHz under turbo. AMD might have improved the IPC improvement on Ryzen, but it's not that clear in PUBG. If I were AMD, I'd be reaching out directly to Bluehole and working with them hand-in-hand to provide Ryzen specific optimizations, especially with so many threads available on mid-range chips like the 1600X."

I would never build a system around one game, especially one that's not finalized. It may or may not see benefits to extra cores, but MULTIPLAYER games do increasingly seem to benefit from more cores. Not sure what state PUBG is in today since this article but I know it's nowhere near final.

*I always plan for the LIFE of the computer. I think the R5-1600 is an excellent CPU. You may reduce the FPS in some titles, but generally can usually get 60FPS, and the CPU should last much longer than an Intel i5 as time goes on and programs become more multi-threaded. Especially now that DX12, Vulkan are taking off and game engines like UR4 are incorpating these API's better and allowing easier access to multi-threading (by having it built increasingly into the game engine code).
 
Solution