That amp puts out 600w x 1 @ 1 or 2 ohm mono.

I'd recommend you stick with two ohm mono. Therefore, you need a pair of subs that are either single 4 ohm, or dual 2 ohm coils.

The amp puts out 600W, so a sub that handles 300W RMS would be appropriate. That's a recommended number, and you can go either direction and be smart.

As for a sub suggestion...it all depends on what you want, how much you want to spend, and how important trunk space is to you (you didn't read the sticky did you )