Hey all so from the internet searching I did I found reccomended 0.126" up to 0.128" balls to replace. I ordered up some 0.126" bearings on ebay and they came in yesterday. My z-axis is relatively easy to access so I gave that a shot this morning. I installed one set (each ballnut has 3 sets of 17) and it was way too tight. So I took them back out and measured them. they ranged between 0.126" and 0.1255" (yeah I measured all 100 more than once.) I had enough to try a set of 0.1255" balls but they were still much too tight.
Before I reassembled I measured the stock BB's they were 0.1245". I was thinking about ordering some 0.125" BB's but saw there were alot of other options in between (0.1248" for example). I'm curious, of the people who have done oversized BB's how much oversize did you go? My backlash is about 0.0045" on each axis.