Thank you a lot for answers.
I also can buy same card with 4GB for only $20 cheaper. Therefore, 8GB version is better option I think.
Also, I'm a little scared if GPU will be good, when ETherum will go PoS.
First time I want buy 1080Ti GTX cards for $1000, but I can buy only 4. Rx470 I can buy 12pieces for same price and have better ROI.