Thankfully it was posted to HN so I could find it. Google search has a truly become useless for this stuff. It's early in the morning, but I think I'm reading the abstract right. [1]
To add some anecdotal info, those numbers are much more closer to my own personal experience. I've been experimenting with various dosages, with regular blood tests by a doctor, for a few years now. Currently I've setteled at 4000 IU/day to stay at 75 nmol/L, which is the lower end of what is considered normal.
1. https://www.ncbi.nlm.nih.gov/m/pubmed/28768407/