Dangerous question around these parts, and there's a few different answers you'll get:
Some will tell you it's plenty, since Ford designed the engine to run on 2" pipes.
Some will tell you that vehicle manufacturers often cheap out on exhaust systems, and are known to hang restrictive exhaust systems on vehicles to save money on production costs.
I say there's no reason to change out new parts if they work.
So, here's an article that explains some details on exhaust sizing. It's a good place to start, but by no means lists all arguments and theories around exhaust systems:
Exhaust system design is more complicated than running a few tubes. Look into the fluid dynamics involved in generating scavenging and avoiding restriction.
www.enginelabs.com
I'm of the opinion that exhaust systems are one of the more difficult aspects of vehicle tech, and that I absolutely do not know enough to advise someone ??