Do fórum do Ars Technica, cortesia do nome de usuário DarylF2:
link para o Ars Technica Forum
I figured it out, and is was actually pretty simple.
Show the package contents for "/Library/QuickLook/iWork.qlgenerator/" and edit "/Library/QuickLook/iWork.qlgenerator/Contents/Info.plist".
Change the "QLPreviewHeight" parameter value from "600" to your new value (I used "1000") and change the "QLPreviewWidth" parameter value from "800" to your new value (I used"1333").
That's it.
I didn't need to reboot or even log out and log back in for this to take effect, but I did need to open a few Pages document Quick Look previews before it seem to "take".
As always, back up the original file first and realize you are editing a file Apple didn't intend for the end user to edit.
Eu apenas testei e funciona apenas para documentos do iWork. PDF e outros tipos de visualizações não são afetados. Vou tentar ver se há mais do que isso.