I mean, you could certainly try MySQL to see how it compares. It's hard to guess in advance because it seems like this is a very specific scenario.

But 40 columns should be a cakewalk for any RDBMS to handle. And I assume you're not storing KB's of data in the different columns? Because if your strings are large enough to be allocated as references to separate blob storage, rather than in the row, that could be a performance problem.

Bulk operations with millions of rows can also sometimes take way longer if you're doing them as a transaction that can be rolled back. If it's acceptable to disable that, that could be a huge improvement.

You can also sometimes find massive speedups in using bulk SQL statements (upserting 1000 rows per query, rather than 1 row per query) or CSV file import rather than SQL.

And obviously make sure you're using indexes wherever appropriate.

Because generally speaking, upserting ~10 million reasonably-sized records is the kind of thing that should only take a few minutes on an SSD. You're not going to do it in seconds, but it shouldn't be taking an hour or anything either.