A bigger motor doesn't have to work as hard. Driving habits attribute much to your milage. Like I said, if you coast around like granny, you'll get good milage in a heavy 4 banger car. But you won't. There will be big rigs to pull out infront of, short merge lanes to accelerate on, slow grandmas driving Camrys to pass.
Stuff like that...I believe you'll see your milage decrease in a car that is as big as the Camry. Of course I'm speculating.

My brother owns a slightly mod'd '02 Altima 3.5 SE with a 5 speed. He drives it fairly hard, he tells me it averages around 22-23 Mpg. Not too bad. Sure he looses a few gallons to the 4 cyl version...but he says its worth it.

But...Charles if you went for the Camry...more power to you. They are nice cars no doubt.