I think, that is a rather complicated question. You should also take into account how accessing other data is affected by large blobs that reside in the same database. For example: you have a table with large data blobs and other tables with conventional relational data. The blobs will take a lot of the cache size away from the other data. Also by increasing the database size, you will have potential longer access times, at least when you use spinning hard drives.

So, several things to think about (make cache bigger, how much grows the overall db size) that can change the database behavior.

Of course those numbers can give some directions, but since only the blob data was taken into account, it can not give full information.

I personally would most of the time prefer smaller db sizes, at least, on edge cases. Relational databases are great for structured data -- unstructured data is not their specialty.