I feel like it would be useful to know exactly how much alcohol is in a can or a bottle. Also why is alcohol the only thing measured in percentages and not sugar or caffeine or medicine?
I would guess about 4% heavier with sugar, which is just enough so that a can of Dr. Pepper sinks while a diet can of Dr. Pepper floats. I think I recall the specific gravity of most sugar flavored soda was around 1.04 but I would need to check sources.