There has been some discussions around other posts on the 426, 440 etc. Here is a pretty good site with a ton of Hemi info plus a ton of New Challenger stuff
http://www.thehemi.com. Back in 75 I had a 67 GTX with the 426 dual quad. I put a set of headers and traded out the Thermoquads with Holleys and added a dual point ignition as the only mods to the motor. The car itself was stock with a 4 speed and a dana 60 rear with 3.91's and I can tell you that this was one of the meanest cars around. With slicks underneath this car would turn just a hair under 13, roughly 12.7's consistantly. I would venture to say that it sure would give todays Challenger a square run for its money and while I wish I had that GTX today..I am sure glad to be getting the 09!!!!