Improving sync write performance in homelab

[sca33]

Running Freenas on bare metal:

AsRock Rack E3C224D2I mini-itx
Xeon E3-1231v3
16gb ECC RAM
6x WD RED raidz2
Fractal Design Node 304
2x sandisk usb pen drives for boot

My raw drive write speed is ~320MB/s.
iperf speed is ~120MB/s.
Write to nsf share speed ~105MB/s on 10GB test file.
Write speed inside VM via ISCSI ~ 32MB/s on 1GB test file dropping to 10-15MB/s.

I'm looking for a way to improve my write/read performance inside VMs via ISCSI.
I know that ZFS needs as more RAM as possible and sync writes would improve with SLOG. My RAM is already at maximum. So would I gain anything by adding SLOG? If so which one to consider using only single available PCI-E slot?

 

[Rand]

Best affordable slog currently would be a 905p/900p.
It might be overkill for your 1G network connection but its not that expensive (especially used).

Now in general the hw is ill suited for a VMware datastore (harddrives, z2 pool), but the 900p might help a bit