How long will it take me to download this from Lightroom Downloader?

I switched catalogs last year and have been unable to use the cloud portion of Lightroom. I haven’t sync’d my catalog because there are a lot of photos I don’t have access to any more that are sync’d currently. 

I found out about Adobe Lightroom Downloader and was able to see the process and get it started. Well it turns out…

“Your Lightroom account contains 811,487 photos, 1 videos, 0 deleted photos, and 0 deleted videos totaling 21.0 TB. Choose a download destination that has enough free space to hold these files.”

I’ve seen people complain about 870GB download speeds… 

Is there a best practice to this? Any tips and info would be super helpful for a download of this size.