Windows 7 user interface to use the Font size of 100% (vs the default of 125%) for custom applications.

User Configuration \ Preferences \ Registry (Right click and select NEW \ Registry Wizard)

Configure the following DWORD key: HKEY_CURRENT_USER\Control Panel\Desktop\LogPixels

Use the values as needed:

00000060 (Small Font Size 100%)

00000090 (Medium Font Size 125%)

00000144 (Large Font Size 150%)

Gpupdate /force a test client machine, then logoff/logon and see the setting take effect.

Preventing users from being able to change the font dpi with another GPO setting:
User Configuration \ Policies \ Administrative Templates \ Control Panel \ Personalization \ Prohibit selection of visual style font size = Enable