A single ported sub will have approximately the same output as two of those same subs in a sealed enclosure off of the same power. This is a generalization. But going ported generally increases output by an average of 3db over the entire bandwidth, and up to 6db-9db at peak frequencies depending on enclosure design.
And the results will be the same with any sub suitable for a ported enclosure. If you want "really loud", it's mostly in the design of the enclosure. But most reasonably designed and priced subs are capable of relatively high output when ported, assuming the enclosure is properly designed.
Kicker L7, RE SX, yadda yadda yadda.