Satalaj, you have to make sure that while running procedures in infinite loop, you make sure that you identify which procedures running parallely are getting the CPU usage up (by parallel, I mean the tasks running in parallel). Also, check the CXPACKETS running as the wait type.

You can also use SQL Server Profiler and also perfmon correlated together to toggle through the database and traces, to see when CPU usage creeps up.

Rgds!!