I know this answer is too late to be helpful to the person who asked it, but I just cooked a butterflied 11 pounder at 325 in my convection oven. It took about an hour and a half. My oven is well insulated, but I opened and shut it a few times, because (lucky me!!) I had a few other dishes cooking on the bottom shelf -- one of the many advantages of spatchcocking. I'm totally sold on spatchcocking. ;o)

Here's a link to a recipe for a 15-16 lb butterflied turkey I think you can use for a guideline:
http://projects.washingtonpost.com/recipes/2007/11/14/herb-crusted-roast-butterflied-turkey/

14lb turkey stuffed should take about 5 1/2 - 6 1/2 hours to cook completly.