Glad to see that someone did mention that there was also the MINOLTA MD TELE ROKKOR 1:2.8 f=200mm lens. And I do admit that, while there are copies of these lenses here, no, I have not yet run any kind of a comparison between them.
As a quick comment, there were never any real differences between the ROKKOR lenses and the ROKKOR-X lenses. That "-X" suffix was only engraved onto lenses that were headed for North America to MInoltaUSA and were marked that way in order to clearly qualify for the MinoltaUSA "M-tag Warranty" program. MinoltaUSA was the major seller of Minolta lenses at that time, and they could ask for that special engraving for the lenses coming to them. They wanted to avoid possible problems with the "grey market" and questions of warranty. They were made on the same assembly line using the same parts that had lens elements coated in the same way. There is no real difference in the way that the two were made. There was one rumor that the "-X" lenses may have received some additional quality control checking, but that is the only thing I have ever found. Please note also that the "-X" distinction was dropped in the middle 1980s.
I've seen a couple of f/2.8 versions around but never had one. If I can find one at a reasonable price I may pick it up..