Have to agree for the video cards with 3.0 capabilities i would go with the z77 which runs both x16 slot at x8 PCIE 3.0.. Fyi you cannot mix the 2.0 card and still have one running @ 3.0.. the link will drop to x8 PCIE 2.0 standards.
If poem is what your optimizing for then for the video cards that run at 2.0 i would sugest going with the 2011 sandy so you can have two true PCIE 2.0 x16 specially for those beast 2.0 dual gpus imo.
I know there are some motherboards with that PCIE chip that allows more PCIE lanes but i dont understand how that makes things faster when it connects to the same single PCIE lane going to the CPU.. Maybe someone can answer this one