Well talking power wise the HEMI "MAGNUM" is rated 100 horsepower more and 30 ft-lbs of torque more than the 5.9L "MAGNUM" V-8 (360CI)! The HEMI is said to get better MPG than the 5.9L as long as you dont boot on it all the time. I have heard MPG from 9mpg - 19mpg w/ the HEMI depending on people being a lead foot or just driving normal. The HEMI is by far quicker than the 5.9L is quarter mile times. However, if you are talking top speed... it shouldn't matter Dodge has all Dodge trucks limited to 118mph top speed or so they say. Ford has a top speed of 108mph and GM has a top speed of 98mph (those are full-size top speeds minus the Lightning)
I'd say, other than the peak torque and HP already mentioned, the LOCATION of the torque in the RPM curve is the biggest difference between the 5.7L HEMI and 5.9L engines. I have an '01 Durango 5.9 R/T and an '04 Ram HEMI. The Durango can accelerate at 1,100 RPM comfortably while the HEMI only feels comfortable above ~2,000 RPM. Peak torque on the 5.9L comes 1,400 RPM sooner than the HEMI (3,000 RPM vs. 4,400 RPM).
I love my HEMI and am going to keep adding performance bolt-ons to it, but IMHO, the HEMI drives more like a racing engine while the 5.9L "360" engine drives more like a low-end grunter.
Disclaimer: My first Ram had the 8.0L V-10, so I may have a warped sense of (torque) reality.