20sq in of port is waaayyy to small for those.
Anyways about tuning, it depends on your tastes in music. I like the 40-45hz range, it's generally very loud and rattles my ears.
It also depends on your sub. In my case, the Audioque HD3 is a VERY unique sub and a biotch to tune. . . I was doing 50hz daily, then I swapped the ports for a 40hz tune and everything almost sounded the same, so 50hz daily for me //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif Not to mention I like the feeling of 50hz notes - hurts your ears, blurs your vision, and you'll really feel it in your chest haha.