I've been running the Spec-R versions since last spring in Mod TC outdoor and 17.5 over the winter indoor. Although they are getting a bit sloppy they have held up wonderfully with many good crashes under their belt. These are about 51mm and do use the narrower inner bearings. I also do find that I need to replace those occasionally but it's not been a big worry.
I did have a set of the xray shafts. Those made it one indoor season and about four laps outdoor before one gave up at the joint. It's a limited test but for my money I'll be using the Spec-R shafts for a long time.
I've never used any of the others so I can't compare.