I would still stick with RAID 10 as that will give you 1.5 TB. If you go with a single RAID 5, you may end up with problems if you present a single array over 2 TB - http://communities.vmware.com/message/829753.
Given you specs for VMDK above, what do you plan do do with the rest? What do you have planned for backup? If you do go with 2 * RAID 5, I would place the databases for Exchange and SQL on different arrays.
