I thought the R5 rear setup was very impressive, like you said, the CRC side links did get sloppy on me as well, and pretty quickly. I think a big part of it in addition to the smaller balls, was that the side links on the CRC's are so short. They go through a bigger angular change with chassis roll and have to put more pressure on the balls when that happens. Associated's R5 side links were longer, so less pressure on the balls as the chassis rolls. A side benefit to this is there's a bigger "sweet spot" in getting the center pivot right... Seems like I had more latitude with the R5 on the adjustment to get the ideal no click on center and no bind at the ends. If the side links do ever get sloppy on the balls, you have the ability to snug them a bit with the screws.
Really the best of everything right there.