I used SO-4 for my Strawberry Blond today for a 12 gal batch. My fermenter is 15 gal and I should have around 3 gal headspace so I'm not worried much about a blowout. I do like this yeast and keep a lot of it on hand. It hasn't failed me yet.
"Look, let me explain something to you. I'm not Mr. Lebowski. You're Mr. Lebowski. I'm the Dude. So that's what you call me. That or His Dudeness... Duder... or El Duderino, if, you know, you're not into the whole brevity thing." -The Dude