Splitting didn't make any difference to be honest. On the BT Hub 6 when I was on BT I split SSID and it did make a difference. I got a constant 50mb on 5GHZ on 2.4 I got around 35mb on this Talk Talk setup doesn't make any difference.
On the Talk Talk hub 5Ghz gives millions of errors, on the hub 4 no difference. I am getting a hub 5 today to give it a whirl.
Out of interest, someone mentioned a Talk Talk trial of firmware to improve wifi etc. I have come across the link in case it helps anyone else.
https://community.talktalk.co.uk/t5/Our-Blog/Calling...