You can keep 16GB of ram there's just no need for the MHz of it to be 2666. the intel I series has very little difference in performance between the Mhz speed of the ram it uses.
For gaming the i5-3570k CPU will preform roughly the same for cheaper.
I love Asus Monitors, Evga Nvidia Gpus, Corsair PSU's. See this site for their monthly Best GPU and SSDs for the price articles. Def get a SSD or 2 =P. I like having a SSD OS drive (Small one works just fine) a SSD for my games and then a large HDD for random data storage.
As far as the Mobo goes, Quad sli shouldn't be a huge factor, Asus is a great brand however. I'm not even sure the newer nvidia GPUs can be quad SLI'ed anymore I think for the 500 series or at least a few of them they could only do 3 in sli. (don't quote me on that i cant remember where i heard that from)
IMO Tri and Quad are for bragging rights.
Also IMO you really don't need to spend more then 2k on a gaming PC(I'm excluding the price of monitor(s) in that figure, larger expensive SSDs, and any other excessively expensive component(s)) any more then that and you're just spending an abundance of money for tiny % increases in performance you likely wont ever notice.
Exceptions being wanting to game with surround 3D gaming which requires the 120hz monitors and very beefy GPUs.