HDS and HDC will work in the same enclosure. Assuming you don't plan to get an HO alt and a few more batts, then get the HDS subs and be happy with it. Going to HDC's alone will not be much of a difference. You will need more power also which will require stronger electrical.
I run 2 SDC15's off an AQ1200 in the wifey's minivan, it's rather loud for a budget set up and stepping up would require electrical upgrades I don't feel like doing....
I run 2 SDC15's off an AQ1200 in the wifey's minivan, it's rather loud for a budget set up and stepping up would require electrical upgrades I don't feel like doing....