How are you loading these files into the SQL Server?
For something like this it is recommended to use the BCP command line tool. When using BCP use the -b flag to have it process the records in smaller batches. This way it will commit the records in small groups instead of trying to commit all the records in the file at once.
I usually use batches of 1000. Using this method you should be able to load in the 50M records within a couple of hours maybe.
If there are any indexes on the table, you can try removing them as this will speed up the insert process.