And have you tried that Mint CD on the problem desktop?
I can only suggest you add your 'font experiences' to the link I gave above @forums.kde.
As kde-desktop 4.9.1 has been released and a few users are still experiencing what appears to be vsync issues, then a bug report would be in order...
Any bug report will be referenced in that link also...
This issue was solved by creating a file named xorg.conf, with the following pasted into it and saved to desktop or wherever:
Once saved, move xorg.config to /etc/X11/Code:Section "Device" Identifier "Intel" Driver "intel" Option "DebugWait" "True" EndSection
If you don't have permission to move it, open the terminal and paste the following:
Enter password, close the terminal, shutdown/restart the computer.Code:sudo chmod 777 /etc/X11
The solution was found in this link.