Actually FedEx won't be affected, they're far busier over the holidays. iPhones are small, light, and the number of units while high for Apple, will only be a small bump compared to others high volume shipments. That's why Apple uses FedEx, this will be easy for them.
It probably depends where you live. I live in an affluent area and I talked to my fed ex driver during the 5 or 5S launch (can't remember) and he said they had a ridiculous amount of iPhone deliveries that day.