I found a useful script to find executions of stored procedure. This will give you a good idea of what is utilization. Run it multiple times to compare how often a procedure of group of procedures executes within certain time periods.
For example, you have a under performing billing process. Your system fires multiple procedures multiple times. You could use something like this to get an idea of execution counts, worker time, average elapsed time and max logical reads. It will point you in the right direction procedure that can be optimized. Tweak this to fit your needs.
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