Hi i’am still learning ue4 and once i feel more confident with it i will upgrade my system to better one i curently have i5 6600k and i think of going into i7 8700k or ryzen 7 2700x.
Is there huge diference betwen them or both will do job just fine?
Either will do just fine. The 8700k is better in single core workloads, the 2700x is better if you have something that can make use of all 16 threads.
I upgraded to an 8700k from an i5 4670k and the difference is quite significant for most tasks. A 6600k is a fairly recent chip, you might get a better performance per dollar increase by upgrading your GPU instead, but if you already have a good GPU then moving to an 8700k or 2700x will give you decent performance increase.
In most games that only use 4 cores you will not see much of an increase, if any, but for gamedev it will make certain things like shader compiling and building lighting much faster.
The difference between the 8700K and 2700X is apparently negligible for gaming (a very slight advantage to the 8700K), but dev work could see a far more significant advantage for the 2700X.
If I was looking now, I’d get the 2700X, especially with the PCIE limits of the 8700K.
Chiming in here, just get the ryzen. Seeing the lighting build running on 16 threads is somehow very satisfying 
Thx so 2700x on average is better for ue4 than 8700x, @ don’t belive gpu upgrade would be needed in my case unless i swap to 4k monitor