Yeah, it looks like a great option. Would a 750 be better than 2 650's though???
No, but there is a 750M SLI option available though. It was slightly out of the price range you listed though so I didn't link it. A single 750M performs about the same or slightly better than a 660m. Two of them in SLI would be pretty insane performance for a laptop of this size. Or think about it in the Y400. More powerful than a lot of the huge and heavy "gaming" bricks on the market in something that weighs under 5 pounds.
Lenovo has really done something with the Y series.