overclocking'" "amd ryzen threadripper 1950x

I am thinking of this set up but I am still struggling with my memory choice. CPU: AMD Ryzen Threadripper 1950X MOBO: Asus ROG Zenith Extreme MEMORY: Corsair Vengeance LPX CMK32GX4M4B3200C14R (True latency 8,75ns) Donnow where the 'R' stand for btw? I am aware of these compatible memory...