What always hurt the Hemi in the street car crowd was the inability of most owners to keep them properly tuned. Most that you ran across back in the day were still running the same tune that came from the dealer. They rarely if ever kept the valves properly adjusted, they never tinkered with the carbs and step up linkage to get them to work better -- they did good just to change the spark plugs and oil. Most owners didn't understand the Hemi's needs. You have to stay on top of them to keep them running up to their potential.
The second issue that hurt the Hemi's was the cubes under those heads were too small to take much advantage of the higher flowing heads and better valve layout. To make them perform, you had to make them rev. That's when they wake up -- RPM.
To illustrate my point:
440 -- stock #452' flow 264 cfm at .500 lift
440 -- stock #906 flow 270 cfm at .600 lift
440 -- stock #518 flow 295 cfm at .600 lift
And: 426 Hemi -- stock flow 355 cfm at .600 lift
With that information you can see that the Hemi heads need one of two things to perform up to their potential:
Cubic inches under the heads OR rpm with smaller (426) Cubic inches.
Here is a handy Cylinder head flow information chart that has all you would ever want to know about head flow on these old Mopars:
http://www.mopar1.us/flow2.html 
