Your assumption is pretty much correct. Infinity subs are mostly SQ subs. Especially the lower end reference models, they will sound good but won't get really loud. However, The perfects are pretty good at doing both jobs. They have good SQ and can hit pretty hard in the right enclosure. I personally like more punchy bass so if you like that go with a small sealed enclosure. If not, then check the specs and make up a nice ported box.
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Ron Jon