Im tasked to investigate a stored proc that is slow at certain times ( 20-30mins ) and fast at other times ( 10-15 secs ).

After following suggestions i found out that adding NOLOCK hint on all the select queries makes the execution time fast ( 10-20 secs) .

Although i know that adding NOLOCK means a dirty read of possible incorrect data, does it justify the performance boost?

Speed or data correctness?