A customer report that the NFS performance result for NFS 16K Writes are - 11 MB/sec.
The tests on the DSS Demo (Atlanta) and IOMeter, while doing 16K Reads and with the parameters as specified in the attached "Comparison of Storage Protocol Performance" from VMware, for iSCSI and NFS are 110 MB/sec, which match the document. The performance for 16K Writes on iSCSI is 70 MB/sec. But NFS performance on the write is very slow.
Based on his tests; and by unchecking the "Synchronous" box and ran the IOMeter write test reported 100 MB/sec -- the same as for iSCSI. Also, customer cloned an 8 GB VM and the results were comparable to iSCSI clones -- just under 3 minutes or 50 MB/sec.
In VMware forums they advised against using asynchronous mode for NFS because power failures and other failures in the storage server could corrupt the NFS volume. They did say that if your RAID controller has a battery backed cache then the danger wasn't high but they nevertheless recommended running in synchronous mode.