One Wyeast pack, or two?

I'm brewing an imperial stout and I'm trying to decide how much yeast to pitch. It's a 3 gallon batch (on account of mash tun being unable to hold enough malt for 5 gallon high grav batch) with an est. SG of 1.066. I'm using the Wyeast Pitch Activator packs. Their site says you need one pack for 5 gallon batches with an SG up to 1.060, so I'm right on the line of needing two.

Any suggestions on 1 vs. 2? Main concern is over pitching.

(And I have no DME on hand to make a starter.)

 

one pack of yeast most likely would be an under pitch. Two packs of yeast could also result in an under pitch. The number of viable yeast cells in a pack depends on the production date of the yeast. The moment the yest is packaged viability begins dropping. Mishandling will drop the per cent viability even more.

Put your numbers into this pitch rate/starter calculator to see where you are with the yeast you have.
http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

If you do need to make a starter, there is a way to make one without DME.