You need to obscure your email account login info in that pic.

In that pic, do you see the Name and Value boxes bottom right?

Click "New" above them.

For maximum foreground window FPS of 10:
Name: maxfps
Value: 10

For max background window FPS of 10:
Name: maxfpsbk
Value: 10


Then load your WoW clients and they should all use the desired settings.