Hmmm I had this problem while I was using my studio G3 (semi opaque) 21" studio display with MS. - The studio display hasn't got manual display dimensioning and the soforth. Luckily I was able to find a refresh rate and resolution that almost fills the screen properly.
Now I'm using Kubuntu instead on the same monitor. Sadly it's refresh rates and resolutions that are selectable are unsuitable. - in all cases theres up to 3cm worth of black bordering the output.
Should I use xvidtune to try and change things, or can I make manual adjustments through xorg.conf.
-If xorg.conf is the only way to go I guess I'll have to make up values in there. (I think there is the next higher res but less bpp that will make everthing looks as it sort of should)
--but is there some sort of may to do manual dimensioning for the xserver's output , eg width height, rotation etc. ie just like the original os9 mac software driver could do?
ps - it's an offf the shelf standard g3 450 yosemite PowerMac.
Any suggestions would be great (I don't want to buy a flat panel just yet - besides it looks great having a neat g3 with KDE on - shame it's not on the screen properly)