Extract values from the String filed in SQL server

I have large table with around 50million data that needs to be updated and inserted into then final table. My approach was to apply transformations and then load into temp table and finally loaded data from temp to permanent table. But this is taking more than 10minutes to complete. I tried with few other options that was recommended by other folks but nothing has been worked out.

Thanks! 

Is the data type of the primary key of the table is int or bigint? If yes, you may split rows into several subsets. That may improve the performance. 

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