If you're worried about them not being fully cooked you can always get a meat thermometer. That's what I use. And it does usually end up being about 45 minutes for 9 breasts.
Although I cook at 350 typically. And the pan you're talking about is fine.
One thing, Costco has some pre-flavored chicken breasts for about 3.70 per lb. Comes in three varieties, lemon herb, teriyaki, and mediteranian. They taste great, have a lot of flavor, and really don't have any extra noticeable carbs or anything. They are just fresh packaged breasts with marinade in the package. Pull out, cook, and have a super tastey chicken breast! They usually come in a pack of 9 breasts.
Just a little tidbit on easy flavorful cooking.