I don't know the specifics of AOC's hardware requirements but at 19x12 SLI will definitely be noticeable.
But remember that you're spending $150 dollars extra to get an SLI ready board. If you wait for the GT280, it is supposed to be better than two 8800GTS in SLI (I think..we'll see). It may be more expensive than the two 8800's but with the money saved by going to a d3sl you could probably fit it in the budget. Something to think about