Welcome to the community!
First you need check this matriz of compatibility http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003212
Second i recommend enable hyperthreating because in general its considered best practices.
And to enable EVC you need power off all virtual machine, you cant enable evc with virtual machines running. ( http://pubs.vmware.com/vsphere-51/index.jsp?topic=%2Fcom.vmware.vsphere.vcenterhost.doc%2FGUID-DE575FB9-24AE-4453-966B-5340B8147FC9.html )
considering that you´ve a vcenter in vm check out - http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1013111