Three games to go and 49 points with goal difference is not an unreasonable realistic requirement to finish 21st. On this basis Preston are already safe... just.
Luton and Plymouth have the run ins from hell playing teams at the top still in play off or automatic promotion fights (and not Sunderland who are already safely in the play offs).
The others all have eminently winnable games on paper so it comes down to ability, grit and momentum. On yesterday's showing, Derby don't have any of those qualities so they will join Luton and Plymouth preparing for a trip to Burton next season.
Up top, the dingles and Leeds have the automatic places sewn up barring losing two of the last three games. Similarly, Bristol City and Coventry have to implode not to get 5th and 6th between them.
Boro have to go to Coventry on the last day of the season with Coventry visiting Plymouth and Luton before then so even a slip up against those two relegation haunted sides means Coventry still have 6th place in their control.