i had G-Skill Ripjaws (2x16GB) 3000 MHz in A300 with 3400G and works fine with 3200MHz. [G.Skill Ripjaws - DDR4 - SO DIMM 260-PIN - 3000 MHz / PC4-24000 CL16], because I had flashed P1.30S, what is support 1.2V and 1.35V for RAM, too.
In X300, I using Crucial Ballistix (2x16GB) 3200 MHz before...