Ok, final update on this. Ignoring the covid year - of the 57 teams in the relegation places after 42 games, 53 end up getting relegated so if you're in there now, it's looking very bleak.
In term of points only 2 teams with 48 or more points after 42 games have been relegated (in the same season 2013 - Wolves in 23rd, 48 and Peterborough in 21st with 50).
In terms of positions, no team in 17th after 42 games has been relegated. The closest is Gillingham in 2005, who were 18th with 47 points but ended up relegated with 52 points. At that point though, they were only 2 points clear of the bottom 3, not 6 like we are.
So, in conclusion, it's basically done - we're pretty much safe. I know there'll be some twitching about this, but it would take a very unusual set of results for us to get relegated from here.