Been getting the same warning emails (200GB in my case). So I tried this now, but it doesn't seem to highlight anything after pasting in the gist into Chrome. Does it work for you?
If you have a Windows machine lying around, the iCloud app lets you download all your media out of iCloud Photos. Once it's all on Windows it's a lot easier to find the largest files!
You can also do that with Photos (leaving "optimize storage" off) and downloading all to your Mac, I believe. I haven't actually done yet that since it is quite a large download.
