in my country (iran) you have to pay more the real price for example if a MB is 300$ in amazon I need to pay about 350$ for it. and i5 8th gen good models are not available in Iran yet. So which MB should I buy for a i7 8700k(without bios update)? And do you think 8700k will be compatible with 1060 6gb OC for gaming (no bottleneck or this kind of stuff?)Is there a particular reason you want to go with 6th or 7th-gen instead of 8th or 9th-gen Intel CPUs? An 8th or 9th-gen i5 is as fast as or faster than a 6th and 7th-gen i7 and therefore more cost effective.
my pocket is the main reason for choosing this generation. I need to save my money for a year so that I can buy a i7 8700k with asus prime z370a.Even though your components appear to be compatible, I would suggest you go with the 8th generation Intel motherboard and CPU.
There will be not upgrade path on the 6th and 7th platform.
You need a reliable PSU. What's the model of the PSU?
I bought my gpu(1060) before.As you can see, the graphics card will typically make a much larger difference to gaming performance than the CPU, so it's probably worth spending more money on that than on the CPU and motherboard. Even something like an i5-8400 on a B360 motherboard with a GTX 1070 should generally perform better than an i7-8700K on a Z370 board with only a GTX 1060, at least as far as gaming is concerned.