Shadow, upgrading bearings does help with casting distance especially the ceramics. However, IMHO, the most important thing is the care and maint of thestock bearings in your reels. The stock bearings are ABEC 3 and the upgrades are ABEC 7(the higher the numer, the tighter the tolerance, therefore a tad bit better bearing) We have seen reels come nto shop flooded with oil or grease or both. too much is not good and prohibits the internal balls from going round raceway, they get bogged down in the sludge. The ceramics do improve casting distance and the ceramic balls inside will outlast the raceway. If by chance, you purchase any ceramics, be sure they are ABEC 7 and have a marking on outside such as CB or C. The ceramics are pricey and if I were you I would ask for a inspection slip or something to re-assure you they are what you are buying and be sure to purchase dry.
anyway, you are brave, I would be afraid to remove anything from the closed bearings. Shimanio has come out with a new anti-rust open faced bearings and they look really good. I do not know the rating on them, I'm guessing a 5.
good question,hope i've answered it ok, i know lots of good anglers on here will be helpful also. conniek