From what I've read so far I'd go with the GTX 560 all the way. It's quieter and less power hungry than the 4 series cards and has excellent performance (sits in between the two but bests the 470 on occasion). Looks to be an excellent overclocker too.
I have a spec in pre production an have ordered a single 1536MB NVIDIA GEFORCE GTX580 card. Would it be better to double up on the GTX 560's instead? If so - the 1gb or 2gb one?
in the short term i think i am right in saying that two 560's would outdo the 580. However it is good to leave space to upgrade in the future where (when you could afford to) you could install another 580 in sli and blitz ahead for a bit longer
I saw this thread and amended my order with PCS which is still in pre-production, hope its ok. After I saw they featured WoW Cataclysm for this new card I had to amend my order as that is my primary PC game and I have been stuck on the lowest graphical settings for the past 5 years on my ancient machine.