K, so It sounds like you have your answer. What I guess your asking is how you can get more throughput out of your iscsi fabric? The answer to that would be to add another network card and vmkernel interface then bind that as another interface to your iSCSI software intiatior. Or... you could look at the application side of things and try to tweak your database server. Normally SQL uses less disk I/O if you give it more memory. However, im not a DBA to help you with that but it's just a thought.
Also, you might want to take at this link: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1029273