Quoting from the Emulex official announcement:
Emulex Corporation today announced the results of an independent evaluation report that compares the performance of Emulex HBAs to that of QLogic HBAs in VMware ESX virtualized server environments. The report by Demartek, a firm specializing in independent analysis and lab verification testing of server, storage and security technologies, found that overall, Emulex HBAs outperformed QLogic HBAs in 2K, 4K and 8K block sizes with four guest operating systems running in a VMware environment. Several characteristics were measured, including I/Os per second (IOPS) and Megabytes per second.
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The Emulex HBAs were up to 9% faster in read IOPS, 31% faster in write IOPS and 31% faster in total throughput at these block sizes referenced. These block sizes in particular are commonly used by Microsoft Exchange Server, Microsoft SQL Server and Oracle databases…
Read the whole performance comparison here.