I immediately noticed a rattle with quick y adjustments on my printer. So I went out and got some Misumi LM8U bearings and matching rods. Yes, I learned after most people use LM8UU. However, I don't notice any real difference from stock to after market. I did a little test and set each type of bearing in my little vice (without crushing) and checked how much slop there was with one end of the rod while pushing gently side to side at the cantilevered side. Each bearing/rod combination has several millimeters of movement. Am I just overthinking this, or should these combos have no slop (or at least almost no slop) in them?