at whatever the resonant frequency is at least. different speakers will have different responses at different resonant frequencies depending on what their own resonant frequency is as well as their own frequency response.
a higher res might be louder above the tuning... but a lower tuning will hit deeper which will probably make it seem to have more impact.
the purpose of a sub is to dig as deep in the bass as possible isn't it.
personally... i think that SEALED boxes hit hardest as the air spring makes woofers hit FASTER. they don't play as deep or loud... but they punch harder.
sealed woofers go *boop boop boop*
while ported ones sound more like *woo woo woo* to my ears.
i can't stand ported woofers. i like smaller faster woofers best short of lightning fast planar home speakers.
to me speed and clarity = a harder hit, while ported fans think that volume and extension = a harder hit.
surely someone who replies next.. will have the exact opposite opinion. the best thing to do is listen for yourself and decide what you like.
if you're 100% for a ported setup... just try an adjustable port that will allow you to adjust your port and resonant frequency to your tastes.
if your who i think you are and your going to run a high ported box at 50 hz and a sealed box for the lows then i want to point out that each speaker will need to be crossed over at a different point. The sealed at 80 hz low pass and the ported will need a special crossover to filter down below 50 hz and only allow up to about 80 hz to match your sealed box. Maybe someone can help you with ideas on that.