Just a few thoughts, since I'm not very familiar with the MSA.
- did you run esxtop to find out whether the latency is kernel or device related (see http://kb.vmware.com/kb/1008205)?
- do all the LUNs on the MSA have write-back cache enabled?
- how did you do the Windows copy tests? Other than ESXi, Windows uses OS based caching, so you may want to use tools like iometer for testing..
André