I know that Standstill is quite the opposite of a Tempo-card. However I believe that my lists needs Standstill in order to coop with the 2 card combo and the possible thread of going 2 for 1'd.
There are however several positions in the board where Standstill would be really great to drop even without a clock.

I don't think 4c Dreadstill is the way to go, clearly. Dark Confidant + Swords + Goyf is a fine combination of cards, it's just too much of a stretch if you ask me.

Furthermore, I don't believe that Cb/top is that important against Zoo. From my experiences with either Dreadstill and Countertop is that it's too slow. It's just too slow. I'm not even mentioning that your opponent might have played Nacactl and Qasali Pridemage/Tarmogoyf before your deck get the Cb/top.
I believe that Zoo won't be played enough, so therefore I might want to play this deck. I'm pretty sure the matchup is weak even with Cb/top.

I also believe that the original deck focusses to many on different strategies, either:
Dreadnought/Stifle
Cb/top
Standstill/Manlands

I'd prefer cutting one to get a more stable deck. I believe Manlands are a good call in this metagame, as is Standstill. Especially when boarding 3 Pithing Needle's against Vial decks.

So,

Conclusions:
Perish is bad against VVsurvival
Hibernation is good against VVsurvival
Perish is good against Zoo
Hibernation is ok/bad against Zoo

Are there any other sideboard cards that might help the Zoo matchup? I believe I have some open slots (1 Vendillion Clique, 1 Crucible) are the most likely to be unnecessary.