Subwoofer question, which one will hit harder?

I have 2 kicker subwoofers that are 300 rms together at 4 ohms. My amp is 300 at 4 ohm or 500 at 2 ohm. I was thinking about switching and getting a alphine 300-600rms at 2 ohm. Would it be worth it in bass difference? What's the difference between a sub that is at 2 ohm and then the exact same sub at 4 ohm?