The DDR3 X 4 debate for me is really s debate centered on The CPU. Do you intend to upgrade to Skylake or Haswell-e? Personally I don't see any advantage for everyday-use/gaming on letting go of your i5 4590 for the time being. It has a respectable clock and a lot of power, enough for most stuff you probably use it for.
Whenever you upgrade your CPU ( and that could be as early as 2016 or as late as 2018, really) you will be moving to DDR4. Until then this is a non-issue for you.
(Not to mention the real,advantages ddr4 brings to the table are more noticeable at higher frequencies which are much more expensive)