Ok, so I've possibly answered my own question! I bound the networking card to VIFO and the system then automatically switched all the network setup to the integrated NIC on the motherboard, it hasn't crashed since, 8 days and counting! So it looks like it was the TP-Link PCIe card, one of the only original cards! The RAM is original but tested ok, I'm replacing it anyway and doubling the amount while I'm at it! That'll teach me to use TP-Link stuff, I've always had trouble with it, bad firmware usually! I guess because I kept reading about all the networking issues around Macvlan I was wrongly blaming unRAID! Thanks to those who helped and made me think to check over the hardware again!!
Cheers,
Tim