The 260M is a G92 chip, not a G200 chip, so calling it a 260m is a bit misleading. Even so, two of them in SLI is certainly faster than a single 4870m. Still, a mobile core2duo would probably be the limiting factor for games which is why I would rather go with an I5 and 4870 in a laptop, but that's just me.
I agree that its a G92 and naming it as 260M maybe misleading but that's what Nvidia calls it.
It mostly depends on the resolution though,if its 1920x1200(which i think it is because its an AW M17x)having a more powerful VGA helps but as i said we need to know the models