for best gpu

Solution
Generally the differences are in the clock and/or memory speeds.
A faster clock will allow for slightly higher framerates.
Buy the fastest you can afford.
thanks for the replay.....1 more thing.....gigabyte z270m d3h or gigabyte z270x ultra gaming motherboard should i pick?.....and i have a powersupply which has 6pin pce connector....but g1 gpu need 8pin connector......my psu tharmaltek 450wt....should i use a converter from 6pin to 8 pin for my gpu?