There are several factors that you have to think of.
1. There has not been much of a difference between gen 2,3,&4 lga 1150,1155 CPU's Except later ones have a few more instruction sets,
2. Running a GPU at PCIE 3.0 X8 makes no difference than if you were to run it at X16 - i can say this from Experience
3. DDR4 will be a worthy upgrade but there is no telling if DDR4 will be released at the same time as the motherboards capable of using it
4. The Extra cores of lga 2011 will almost be of no use to you unless you are doing more than gaming, as of now few games can make use of more than 4 cores, however if you are doing video rendering and content creation than you will want the extra cores.
so in the end its all up to you, if you build one now u'll have it sooner but if you wait you may get better performance, however if the trend stays the same you will see no major difference.