Yes on the outside the Challenger is a lot larger than a Mustang, 10" longer, 8" wider. 3" taller. It also has much longer overhangs than the Mustang, especially in front. So far it doesn't look like the interior is significantly larger than the Mustang. And it will weigh 600 - 700 lb more than a Mustang GT.
The point is the market for a HUGE, HEAVY car that only comfortably seats 2 people and gets horrible gas mileage is very limited. If DCX does bring out a new Challenger, my prediction is that it will have a very short production run (just like the original Challenger) because no matter how cool the new Challenger looks ( I admit it does look real slick ) the market for such a car is very limited, especialy with gas prices where they are.