Buying a Bigger Amplifier for Upgrading Later?

I want to get the Rockford Fosgate T1500-bdcp for 2 kicker L78 Qclass subwoofers (1000w rms combined). And maybe sometime in the future upgrade to 2 L710 Q class (1400 rms combined).

If I plan on upgrading later should I buy the bigger amp now? It would be the T1000-bdcp vs the T1500-bdcp.

Also would this damage the subwoofers or can I turn down the gain enough so I can convert 1500rms into 1000rms. And would the draw from my battery be significantly more for the bigger amp if they are both using the same rms?