I agree when you are talking about picking between 38th to 40th vs picking around 97th (as of today) or picking in the say 139th t0 148th range (as of today) Of course it makes sense that you would rather pick higher at 38th then 40th but that 4th vs 5th rounder could be as high as 51 spots higher.
Not sure about your math, Habs will at best finish 3rd worst, so that's pick number 3 in round 4, the only way we get the 5th round pick is if LA misses the playoffs, so at best they finish 15th (16 teams that make playoffs, will pick after them). So the biggest difference will be 31 + 15 - 3, which is 43.