After reading around I decided to go with:
Instead of a dual 4 ohm sub, I went with a dual 2 ohm sub, so it can take full advantage of the 600RMS at 1 ohm provided by the Amp.
Hifonics Zeus 12" (Dual 2 Ohm, 500RMS max)
Hifonics BXI 610 (mono, 600W RMS @ 1 ohm)
Will the above two work together??