I don't think DDR4 is at all worth the money given your price point.
Here is what is, in my opinion, the optimal $750 build (sans case, psu, OS, and peripherals)
CPU: Intel I5-4690
CPU Cooler (If you can use your old one, great): Cooler master hyper 212 evo
Mobo: ASRock Fatal1ty Z97 killer (ATX-LGA1150)
Ram: Any DDR3 2400. I personally would grab g-skill ripjaws X or corsair vengeance but really there are plenty of totally fine options.
Video card: MSI GeForce GTX 970 4GB Twin Frozr V
Total price: $769
Without CPU cooler: $739
Obviously if you plan to overclock you'd need to change the CPU and Mobo, but really, that is a personal preference and not a huge money changer.