Here's the registry key for it
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\VisualEffects\VisualFXSetting registry subkey.
0 = Let Windows choose what's best for my computer.
1 = Adjust for best appearance
2 = Adjust for best performance.
Further research indicates that "if it can be done in regedit, it can be
done in GPO" - but I don't use Group Policy, so I'll leave that for others!
:0)
- John