A question regarding the DAG size on ETC as well as ETH which is 3gb atm, at this rate the 4gb limit will be around December 2020, is it smart to get used xfx black edition 570 4gb for $80?
depending on what is your elec costs, but you will get a ROI out of that sooner or later for sure, cause at the end of the 4GB ETH mining era, you can continue to support other mining coins and get profits after December 2020
so, the answer is yes.