Tonight I learned that carapace before speed is really really really good vs marine pressure openings....
slow lings with +1 armor do way better vs marines then speedlings without any armor.
They actually do better vs marines then +1 attack speedlings, if the marines don't try to run away etc....
The issue is there speed and the difficulty in getting surrounds with out speedlings.... but your going to get speed shortly after anyways.
Here's another weird tip that sounds like it can't work but it does.
+1 carapace with lings is better then +1 attack vs unupgraded stalkers as well.
BUT +1 attack is way way better vs stalkers if they get the armour upgrade. I'll leave it to you as an excercise to figure out why.
I would go as far as to say that evo chamber at the same time as your pool hard counters marine + tank openings and pure bio openings. (NON-reaper)