Skylake DDR3 capable motherboards tend to be budget class.
You will need a better Z170 based motherboard to overclock a "K"
Actually, DDR3 and DDR4 perform similarly.
But, the DDR3 ram supported needs to run at 1.35v or less.
Most ddr3 1600 ram currently in use will be 1.5v and not supported.
Ram is cheap enough so plan on buying DDR4 ram that runs at the stock 1.2v. That will probably be 2133 speed or 2400.
Faster ram will take higher voltage.
There is very little benefit for most apps from ram faster than 1.2v 2400 speed.
http://www.silentpcreview.com/article1478-page1.html
I also suspect that running ram at 1.35v will have a negative impact on your overclocking potential for the multiplier.