The specs of the Tempo Coax in 6.5" pale to that of the specs of the Polk, and I'm pretty sure that at $100/pair for the Polks (& the added fact that you don't have
to replace the headunit or buy an amp just to drive them, like the Tempo Components), it's quite a value. Just sayin'.
I have heard good things about CDT speakers as well. The base model Firebirds received 4 speakers TOTAL, with single voice coil coaxial speakers, powered by the headunit.