I ran both models, in 'pure stock' form, and many of my friends ran both cars as well.
Since my father had a machine shop "Valley Motor & Machine' in Jefferson Valley, New York
- we saw many of these Stock Mopars run at Dover Drag Strip.
A friend of our's named Dominic, bought a new a 1968 '383' Road Runner (Pillared Coupe) with
an Automatic and 3.23 Gears in March of 1968 from Meadowland Chrysler-Plymouth in Carmel, New York.
In stock trim, and classed in E/SA, it ran 14.85's @ around 95 MPH.
After wrecking the car soon thereafter, he bought another new 1968 '383' Road Runner but a (Hardtop)
with an Automatic, and with the 3.55 Performance Gear option.
In 'stock trim' with 7" Cheater-Slicks and Headers, he got into the high 14.50's.
Those numbers are fairly accurate for a Stock 1968 '383' Road Runner with an Automatic.
Decent performance, but in no way a 'Dominant Street Car'.