As per the recommendation in this topic (http://software.intel.com/en-us/forums/topic/385319), I have used this sequence to disable turbo boost:
"section 220.127.116.11 OS Control of Opportunistic Processor Performance Operation (Vol. 3B page 14-5 of the May 2012 version)
System software can temporarily disengage opportunistic processor performance operation by setting bit 32 of the IA32_PERF_CTL MSR (0199H), using a readmodify-write sequence on the MSR. The opportunistic processor performance operation can be re-engaged by clearing bit 32 in IA32_PERF_CTL MSR, using a readmodify-write sequence. The DISENAGE bit in IA32_PERF_CTL is not reflected in bit 32 of the IA32_PERF_STATUS MSR (0198H), and it is not shared between logical processors in a physical package."
Source: Patrick Fay, Intel
However, my Intel Xeon X5650 (http://ark.intel.com/products/47922/Intel-Xeon-Processor-X5650-12M-Cache...) is still operating at its maximum turbo frequency of 3.06 GHz. Is there something else that I need to do to disable turboboost?