buying under-rated 1000w amps for efficiency is like buying a super charged v8 for fuel economy.
1000w+ is going to cost you some current no matter what you get. It's a class D - its efficiency is probably average among class D's, and I've yet to see a standard method of specifying efficiency so you can compare apples to apples.
If you want a relatively efficient 1000+w I'm sure the Kicker is about as good as anything.
If, by efficient you just want a good amp for the cost - I'd say the zx1000.1 at OCS is a great deal.