That GX2 price is tempting. I thought about snagging one to use until the dust settles. However the 260 is current, single gpu, and offers a nice memory interface. It's cool and quiet (even at load it's managable).
I think it comes down to your primary usage. If you mainly play fast twitch shooters, the GX2 may be a nice option. If you play a mixture of shooters and RPG's that load large areas and textures (Oblivion, Witcher, etc), you may benefit from the extra memory of the 260. One additional benefit, 2D/low power. The 260 is a kitten at idle, very nice for surfing.
If you're planning on buying EVGA (great GX2 and 260 prices), you'll enjoy step-up option with either card, so you're kinda covered either way. Me, I'd grab the 260 even though the GX2 is an amazing card for that price. Good luck..