Any migration is likely to slightly change the performance of individual queries in the application and in stored procedures and functions. Depending on the context, those small differences may not matter in reality. But it is a good idea to deliberately compare the performance of operations that are known to be slow in the original system because any difference in performance is likely to be greater. Such testing is usually confined to specific long running ETL jobs and reports. Other performance issues may show up during functional or load testing and will be addressed as bugs.
