I’ve been working on a project lately with a SAP to SharePoint import mechanism. Basically, an SAP export to SQL will be imported into a SharePoint environment daily. During test sessions we’ve tried to import this database and created 13.000 site collections with a total number of 16.000 sites into a single server farm. During this import, about 200.000 list items were inserted across those sites as well.
All sites were based on STP template files, which meant an increasement of the content database of 40GB. It took about 4 days to import, and still the server was running fine and quickly as well. Quite impressive that a large number of sites and listitems is still supported and runs fine.
No maximum numbers are set fixed, but there are some guidelines available for SharePoint limitations. I’ve never imported this many sites before, and I’m quite happy with the test results so far. Just wanted to share that 
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