Sky seem very irregular about their 80/20 offering. You may find that you can get it if you ring them, or contact them on their website chat. I couldn't get it so went with BT. Some hiccups so far, but not too bad, and consistently fast upload (17Mbps of real upload) even when I was only getting 3.5Mbps down for a couple of days (now back to over 40, and I am hoping DML lets me back to 50 or 60 soon). Some of the issues were odd internal wiring (from GPO days, not bad, just different) which the OpenReach installer didn't notice despite my querying it; it would have been the same Openreach install for Sky as well.
If you do go for BT, ignore their speedtester other than for profile information. As I said above, I get real 17Mbps upload, but rarely above 10, usually 8, on the BT speedtesters.
Moved (with trepidation) to BT Infinity 2 for upload speed. Happy BE user for several years.