Not a direct answer to your question,but pro chefs like 12-14 lb gobblers.
If they want 20 + lbs,they cook two smaller.
They start out better,end up better,in virtually every respect.
That being said,you can take a frozen one and set it on your bottom rack.
Shape may have as much effect as weight.
Now folks can take a 30 lb,split the dark quarters off,from the white and start cooking them,early.
Add the white a little later,and get evenly cooked bird.
Toss the backbone,wingtips,etc in the stock pot.
Now in the old smokette,you can take a correctly shape 26 lb gobbler,if you really believe in pushing the envelope,and want to prove you are dumb enough,and brine it with plenty of TQ,or Prague for at least 72 hrs.
You may have to trim a corner,or three,to help wad it in there.
Flip the bird about every 6-8 hrs,and alot yourself the weekend.
It sure won't be the best bird,ever,but it can be done.
Don't ask, how I know about that" dumb enough to prove it can be done".