Are you asking if you had two identical subwoofers, and one was in a sealed box supplied with 1600 watts, and the ported box with 1200 watts?
If you have optimum sized boxes for each design;
I would say that the ported box will be definetly louder, because ported boxes produce a lot more bass in volume, and also have an extended lower frequency cutoff.
The difference between 1200 watts and 1600 watts in almost unnoticeable.
The difference between 12 and 16 watts is the same as the difference between 1200 and 1600 watts.
Why?
Sound volume is increased logarithmicly, not just multiplied by two.