With a 500RMSx1 kicker amplifier, would 2 12" Eclipse Aluminums (450rms apeice) or 2 RE12's (175rms apeice) be better... I will be building a 5 cubic foot box tuned to 35Hz for them. I currently have the RE's and even if I got the Eclipse's would probably keep them but are the Eclipses really good?
2 RE 12's whould be the way to go since you are only playing with 500 watts rms kicker amp. If you had a 1000 watt amp then i whould go with the Eclipe Aluminums. Besides the RE 12's are nice sub with that amount of power.
IF you want overall SQ you will wanna stick with the 2 RE 12's / trust me. Unless you are gonna go all out and buy a new amp. Right now you are probably running those RE 12's perfectly with the electrical system you currently have. Once you start getting into bigger subs be prepared to spend more on bigger amps and eventually a HO alternator and bigger gauge wiring.