While you definitely would see a bit of improvement in performance, it likely would not be nearly enough to justify the cost of a new cpu and mobo. Keep in mind that when running higher resolutions like you currently are that performance becomes more and more GPU dependent, and less CPU dependent (in most cases). Obviously buying DDR3 now and having to replace it all when you upgrade down the line isn't optimal (especially with RAM being so expensive right now), but at least prices for both DDR3 and DDR4 should drop sometime in 2018 when the shortage is currently expected to end.
