Need advice: 318 or 340 for a 68 Dart?

Before you immediately say 340 let me give you the scenario. Just a regular 2 door dart not a GT unfortunately. I drive a lot. This will be my daily driver. It used to have a 6 cyl. It won't be going to the drag races but I want some pep in its step and upgrade it. Considering gas mileage as well, would there be much difference between the two? The 340 is tempting just not sure if I need it. What would you do? I want to hear that throaty growl and be able to have some fun... Can't decide, getting a motor this weekend so please help!