1. Do i need OC capable mobo to oc my gpu,if one have i5 4570 + non oc b85/h87 mobo is it possible to oc gpu?
You can OC your gpu.
2.What's more easy - OC gpu or cpu?(i'm not fan of oc cpu but would like to try oc gpu)
Both are really easy.
Here you must look one build. Maybe you get an idea by looking this "test" build.
http://extremespec.net/gigabyte-ga-b85-hd3-motherboard-review-design-testing-performance/3/
No. Now you can buy really cheap intel xeon 1230V2 / xeon 1230V3 cpu and they work really fast ,cooler and takes less wattage than K serie cpu. So any build is better buy with xeon than 3570k or 4670k. Fast , silent ,cool, really reliable,stable.. You neme it.. It is just better.
It di have HT + 8treads so it is like a i7 for price i5
http://pcpartpicker.com/part/intel-cpu-bx80637e31230v2
And cheap. Because you do NOT need OC able MoBo or huge cooler. Sure you can buy huge coolerand you get build without any fans needed. So go for it
http://pcpartpicker.com/part/intel-cpu-bx80637e31230v2