Overall engine design combined with having 2 more cylinders.
The SOHC motor was made to feel "peppy" in low rpm's to appeal to a large demographic. For instance, the average joe schmoe thinks the SOHC feels pretty stout because it's got a good amount of grunt during low rpm daily driving. The enthusiast likes it because it allows you to launch hard, or pull out of turns hard, etc.
Our high rpm power isn't something to write home about, especially being that we have a V8 but, it's good considering the amount of technology, effort and money put into the motor by FoMoCo.