ADSL Max did not maximise the line
. It was capped at 8128/448kbps though there was an option not all ISPs offered of 8128/832kbps.
8Mbps is 8192kbps.
80/20 isn't a fixed rate anyway, as I'm sure you realise. It's just a product cap, enabling different speed products to be offered at different prices.
The theoretical maxima are shown in the VDSL2 table on this page
. Openreach use Profile 17a. The rest of the reduction from the theoretical maximum will be down to a number of factors, mainly technical in order to provide a fairly stable and economically viable service.
I doubt if, apart from G.FAST, they will offer anything faster as the priority now seems to be FTTP. Which in the end will replace FTTC almost everywhere anyway.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. 200GB. Sync 01/10/18 - 71908/13506Kbps @ 600m. BQMs - IPv4
If you never think of anything off the wall, you'll never think of anything original.