Saddle height?

Are you talking about the saddle or the bridge?

The average bridge height is about 5/16".  I've read the optimal saddle height (from the bridge) is .15".  I like to see more.  If you go too high it puts a lot of force on the front of the bridge and it can crack.  The depth of the saddle slot has a lot to do with that.  Sanding the bridge down reduces the saddle slot depth, reducing how far the saddle can safely protrude from the bridge.  And sanding the bridge down is permanent.  If you get a neck reset in the future the bridge should be replaced to get the string height above the top back to the optimal 1/2".  Before I learned to do neck resets I ruined a couple of vintage FG's by sanding the bridge down to 3/16" thick with a low saddle to make the guitars playable.  That killed the tone and I sold them.  I wish I could have them back to fix them.

But, with the average bridge height of 5/16", when doing neck resets, I make my saddles to stick out between .18" and .21".  Then if there's any change in the future there is plenty of saddle to work with.

So I should aim for a bridge height of 5/16th or 8mm?

The bridge is currently 12mm. If I lower it to 8mm, I should drop the 12 fret height by 2mm which would be close to perfect. I would assume this would retain the integrity of the bridge and not have too much effect on tone.
I am also wondering about original bridge heights as I have a few old Yamaha with wide ranging bridge heights. My favorite, ‘68 FG-110 is about 6mm.
Thanks for your insight and help.