Man - you guys are up way past my bed-time, so I'll chime in now. Saiko - I agree with what everyone else is saying and have a couple more supplemental points (some of which may have been partially addressed earlier):
1. Price/quantity. Packers are usually at least half the cost of flats. The most expensive I've ever seen a packer is $1.38# at Wal-mart Supercenter. So if I can 2x or more the quantity for the price it's a no brainer.
2. Worried about cook time? Don't worry. Buy a 9-12# packer to start. If you're running a steady 225-240, it will take approx 1 hour per pound, and depending on the meat that might even include resting time on the cooler. So get that dino turd on the cooker by 6:00am and you'll be good to go.