Over head cam designs are largely considered more "refined" than pushrod.
The benefit to the design is increased airflow due to the ability to poke more valves in there...resulting in equal power from a smaller displacement engine (which means increased efficiency)...see: Ford 4.6L vs LS4.....
BUT -- when you do it right, like GM and Chrysler(only recently)...it doesn't really matter. We're getting 400hp for the same mpg as their 300hp V8. So.
I don't buy it. When someone brings it up...I laugh at them.....like this:
