I’m gonna have to scratch my head when you say changing the bearings of making reel quieter and smoother are no performance increases.... I’m going to walk you through a basics physics analysis of what is going on when upgrading bearings.
YES, going from stainless steel to ceramic bearings does make is quieter and smoother, but why? What is the source of the noise? The noise is energy from the spool transferring to the bearing balls and inefficiently getting lost as sound energy. This “noise” is a good indicator of frictional forces that are preventing the bearing balls from glide/rolling on the track. Though some may find it hard to observe this increase in performance when upgrading from stainless steel to ceramic, when you look at your reel and a spool bearing goes bad, you can feel it right away! How smooth a reel is dependent on the bearings that stabilize the spool. Shimano reels with infinity drive and x-ship have a bearing on the spool that fit into the groove against the pinion gear bearing. If this bearing is ceramic, whether someone feels it or not, the performance of the bearing has definitely increased. This is because vibrations due to bearings are from rust/deformations of the track/bearing balls. Or right out of the box, it is caused by friction of the stainless ball bearings against the track and fluid forces of the grease that hinder the forward movement of the bearing balls.
Also, lubes these days boast “super speed” which basically means the lube has a lower viscosity which reduces the fluid/frictional forces by only lubricating a thin layer onto the moving parts. This also means the bearings have to be lubed more often. However, some ceramic bearings are so smooth that they can be run dry. However, once you lose the lube in stainless ball bearings, the balls start to degrade rapidly, causing uneven surfaces on the balls and more vibration, which ultimately hinders casting distance, effort needed to cast, and reliability of each cast.
In other words, there is definitely an increase of performance.
be careful when flushing ceramic bearings with acetone or 90%+ alcohol. The bearing mount is hedgehog and zpi are made of plastic and the above-mentioned solutions can weaken/melt some plastics.
Final remarks: ceramic is better than stainless steel. However, ceramic is much more brittle than steel. I have had ceramic bearings go bad. To the OP, listen to @Bassmann86 and go with the ZPI SiC bearings. They are the most reliable and have the best performance.
As for what bearing sizes you need, hedgehog website has bearing swaps sizes for most Shimano and Daiwa reels. If it does not have the info you are looking for, you are going to need to purchase a caliper and measure inner diameter(the hole where the spool shaft goes in), outer diameter (the size of the entire bearing, and the thickness(lay bearing down on it’s flat aide and measure how tall it is).