Ok just a quick update:
DNS relay is disabled, and I restored the network settings to factory default on both consoles, and both consoles now show the ISP primary/secondary DNS server IPs in the network config section

I played an hour of BF3 on the wired console with no issues, and my son played an hour or so of Halo 4 on the wireless with no screaming (which means it didn't disconnect)

I will try wiring both consoles but I've loaned my extra long ethernet cable to my bro at the mo so can't do this for a while.
I haven't had time to check for quicker DNS servers yet but those apps look good
