alt Hacker News+1 to this method. After optimise storage is disabled on the Mac, wait for all photos to download. Then, open the photos library bundle and you'll see every photo there, full res. Copy them wherever you like.
Also, if you leave optimise storage disabled and continue to use Photos, every photo will be cloned in any local or cloud backups of your machine. This strategy creates additional photo redundancy separate from iCloud while still benefiting from library syncing.
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This was my strategy too, but with a disgusting script which quit photos.app, rsync the photo library to a network share, then reopened photos.app so that it kept downloading from iCloud.
Not sure if the open/close is required, but I didn’t want to find out.
Someone gave me a new iPhone (120GB) and a new MacBook Pro and asked me to download all their photos from iCloud. Long story short, after 120GB of photos were synchronised to the iPhone, the MacBook Pro refused to copy them, and now there's no storage left on the iPhone.
Also, Photos on Mac doesn't have an option to download photos directly, so the only valid option Apple offers is to download them through the web interface (max 1,000 at a time).
There is no official way to download iCloud library that is over phone capacity. Period.
Or use the great osxphotos tool that works with Apple Photo’s SQLite database to let you manage all the photos in your library.
https://github.com/RhetTbull/osxphotos