Thanks, nice article. Few comments:

1. Threads can interfere with each other if there are records on the same pages. And this will be a reality unless split is done by the surrogate key.

2. I would go even further in the changes and create differential update: a. first set the comparison of data and find which records really need to be updated. Then do an update only for those records. This technique allows minimize the interaction time. I have similar set of processes running daily and required to do the simple update/insert. Amount of records is about 100,000,000 in total. But in reality only few thousands are changing. Initial process was done exactly the way you describe in article. When differential load was implemented interaction time (e.g. unavalability of the table for the application) was reduced from 5-10 minutes to the few seconds. I do understand that this required an additional work but I think in most cases this is the most proper way to go.