For Wthreads, the iSCSI target employs several threads to perform the actual block I/O to the device.
Depending on your hardware and your (expected) workload, the number of these threads may be carefully adjusted.
The default value of 8 should be sufficient for most purposes.
And this can be only on iscsi target

MaxXmitDataSegmentLength - Sets the maximum data segment length that can be sent.
This value actually used is the minimum of MaxXmitDataSegmentLength and the MaxRecvDataSegmentLength announced by the initiator.

It should be set to multiples of PAGE_SIZE.
Currently the maximum supported value is 64 * PAGE_SIZE, e.g. 262144 if PAGE_SIZE is 4kB.

Configuring too large values may lead to problems allocating sufficient memory, which in turn may lead to SCSI commands timing out at the initiator host.

As you can notice, that changing Wthreads is done on ESX initiator not target, also the same for MaxXmitDataSegmentLength . So the best is to leave them as default or to ask ESX support if they suggest any other value that is better for you.