Scott, no worries cooking up to a 14lb turkey even on a 22.5" kettle, IF you cook it in a pan and/or use the charcoal baskets. I've never had a problem and never used firebricks, either. That's the magic of the Weber grill, in how a simple indirect set-up will cook so evenly, even with the sides of your formerly feathered fare so close to the fire. I really wouldn't think twice about it, ESPECIALLY if I was using the big kettle.
Smoked my bird in the wsm last year, but I'm not gonna fight it trying to get HH this year. I'll probably just make a half moon of charcoal in the kettle with a big drip pan in the middle. Bird in a pan, legs pointed to the coals, and cook 325-350*. This is how Jamie Purviance recommends in the Weber books, and he suggests starting breast down in the pan for the first hour. Weber and Jamie recommend up to 12lb birds for the 22.5", but I've done a little heavier. You oughta be able to cook a pretty big bird in that big kettle, or if you want to cook upwards of 400*, you'll have more space. NO PROBLEM.