RE: Higher Horsepower & Torque for the 5.7L HEMI
The current 300 hp Mustang GT isn't THAT quick (stock ones, of course). I had an 04 GTO with the 350 hp LS1 and it weighed in at a porky 3800-3900 lbs and I had no problem dusting off plenty of current Mustang GTs all day long, so I have no doubt that a 380 hp Challenger would be able to do the same with ease.
Personally I don't think the Challenger is going to weigh 4200 lbs - I know the concept supposedly did, but my "guesstimation" would be around 3900 or so for the production model. Still way too much, I'll grant you, but you can't expect much lighter in this day of all the required electronics, air bags, smart-suspension systems (or whatever you call them).
I think Ford is going to up the hp on the 4.6 to 350 for 09 (or 010), so the 5.7 Hemi's horsepower boost couldn't have come at a better time. I only hope a hp boost for the 6.1 isn't far behind.