fwiw, I don't think your line has been configured for 800k upstream.
It could be BT tech support think your line is 'provisioned' for 800k upstream as you have requested, but in practise, it looks like it is still configured for standard ADSL1 with standard 448kbps upstream on the line card at the exchange.
If you click on the Further Diagnostics button after the first speed test and enter your phone number, it will reveal the downstream and upstream maximum achievable speeds similar to values reported by your Cisco router. I doubt changing your cisco router will make any difference.