How much yeast for Imperial Stout?

Hey guys. I'll be making an imperial coffee stout in the next few days and am trying to figure out how much yeast to pitch.

OG is 1.095 and I am aiming for an FG between 1.020-1.024. I am using the American Ale yeast, and went ahead and got a few packs of the dry yeast rather than using liquid yeast and having to make a massive starter. Mr Malty tells me to use 1.5 (11g) packs, and my homebrew store recommended using 3 packs for a beer that big. I know pitching too much yeast can cause some off flavors, etc. but from everything I've read it seems this only happens when you insanely overpitch.

My question is, should I go ahead and pitch all 3 packs (again 11g packs, re-hydrated)? Surely this wouldn't be too much to produce off flavors, right? My other concern would be that pitching too much might cause it to over-attenuate, though I'm expecting ~75% attenuation and wouldn't expect to get much more than that regardless of how much yeast I pitch.

Thanks in advance for the advice!

I'd go with Mr. Malty. I wouldn't worry about the .5 and pitch two whole packets. Put the other in your fridge for your next brew. No sense wasting yeast.

I agree with Hammy, Mr. Malty probably has a better handle on what's necessary to make great beer than your homebrew shop. Why add an ingredient that isn't necessary?

Is that a typical FG for an imperial stout?

yea, I'd say it's fairly typical -1.024 would give me 75% attenuation. you aren't gonna get too much below 1.020 without some wild yeasts - i've seen plenty with FG's around 1.030-40, but I don't want it to be too cloying. 1.020-24 will give me plenty of body

Thanks guys, I had planned on pitching 2 full packs (i see no reason to ever pitch a half pack and try save the rest), i was just trying to figure out what effects pitching a third pack may have