[Gonsalu]

I fail to see why setting the transaction isolation level to read uncommitted would make any difference to the data load process.

[stonemetal]

Without thinking about it to hard my guess is there is some overhead in tracking what is readable and what is not readable at the higher read levels. Read uncommitted means it doesn't have to track anything.

[Gonsalu]

Writes still take locks. The isolation level is called Read-uncommitted for a reason.