Sorry if this was asnwered before, but couldn't find it. I can't seem to find any groups that usually release really small sized 4k rips like rarbg used to do. Movies went from ~5GB to ~20GB, and I really can't tell that much difference in quality that justifies 4x the size.
Tried some YTS rips, but the quality is WAY worse than RARBGs rips :(
If size is the concern then you are better off sticking to x265 encodes. Personally I don't go above 1080p and use PSArips most of the time.