ESX/ESXi reads/writes to the physical disk with the same size IOs as the guest.  So if you are running Windows guests with 4K NTFS filesystems, the IOs will be as small as 4K.  Similarly, Windows guests with 64K NTFS Allocation sizes and SQL databases will cause larger IOs.  The block size in VMFS is really just related to file size allocation, if the block size is 1MB, then a VMDK file of 512KB will take up 1MB of space on the datastore, but the IO size is independent of that.  So the answer is, it depends on the guest OS and application.  If you have a very homogenous environment, such that every VM is running the same application, same filesystem, and same underlying OS, then setting the page size to match could help.  However, if the guest VMs are mixed OSs, mixed applications, mixed filesystems, you would be best leaving the page size at 8KB.  Hope that helps!
Unfortunately there is so much online discussion of block size used within vmdk files that searches for the underlying block size that ESXi uses on its vmfs version 3 file system or what block size it uses when reading and writing to the physical disks doesn't produce any useful results.  I'm trying to determine what the optimal page size for a Clariion CX4-480 serving nothing but ESXi 4.1 hosts would be but need to figure out what the vmfs3 block size is and/or what size blocks it reads and writes with.  I figured maybe searching for optimal raid stripe size for vmware might help but that was a dead end too.  Anyone know or experimented with it enough to figure it out?  I'll post back what my tests reveal if I end up walking through all the settings. [IMAGE]
Optimal page size for vsphere esxi 4.1/vmfs3 use