I would recommend the LGA 1366 over the LGA 1156.
It is the better platform and more proven platform outside of the LGA 775 for Intel. It gives you the option for 6-cores down the road (the i7 970 is now under $600 and seems to be dropping). It gives you better multiple card setups.. x16,x16, or x16,x8,x8, where for the most part with the LGA 1156, it is x8,x8. This is important specially when running multiple GTX 580's on multiple monitors... you won't see a bottleneck.