Hi
It is a hard question to answer that to be honest as a lot depends on your finances and what you use your computer for mainly. There is no doubt that the X79 platform is going to be the new power base and it will have all the latest goodies attached. The PCIE3.0 itself at the moment I don't consider to be that important as there is no graphics card that even pushes the limits for PCIE2.0. There are also few if any boards that can take advantage of the new spec yet. Obviously though they will come.
It is going to be an expensive upgrade compared to the X68 platform though and that performs very well anyway. Apparently the new X79 will overclock extremely well if what I have heard is correct so it is going to be some powerhouse. Until I get the chance to get my hands on some of the hardware though I am purely going on what I have read.