It can be the motherboard but with one stick in it should run at advertised speed so maybe it is the ram.
The first time I installed the OS I got it to run at rated timing and speed easily but since then ive rinstalled many times and cleared CMOS trying to get things running stable so im leaning more towards to mobo. The RAM has very little fail rates compared to the buyer feedback on Newegg
But I have no idea why Memtest is acting weird. Im kinda loosing faith in that program though