Readynas 104 Win 7 performance issue

More testing done over the weekend:

Average write about 5-6MB/s. Average read is 30-35.

Driving me mad. Can't see any solution. Trying a new NAS (synology) this week to rule out the RN104. 

Again, Windows 8/10 + Mac machines work perfectly (even virtual machines on running Win10 on the Win7 machine). This has only occured since 6.2.5 > 6.4.2 

At my wits end now. I write large files (photographs and video) and 5MB/s is impractical.

I've tried googling and implemented fixed for all known issues relating to slow transfers on win7. Nothing works. Things include:

Connecting the second network adaptor on the 104 and it's the same performance issue through that connection.

Completely disabling ipv6 on router, NIC and RN104 NIC's. 

Resetting the TCP stack  (in case of TCP timing issues)

Disabling firewalls and antivirus

Changing the switch

Scanning for malware (not sure how that would affect write speeds but I did the scan anyway)

Changing the SMB version on the RN104 to force it to v2.1 (win 7 level) but I tried all other levels too (1.0, 2.0, 3.0) and that didn't change anything much.

 
Now, I do have a spare RN104 (unboxed), so if I can find three spare disks to create a RAID5 array then I might try that (hopefully not on 6.4.2, try to make sure it's on 6.2.5 or lower). 

Other than that I'll see how the synology fairs up and take it from there.