Alienware 15 r3 RAM memory

Hi everyone!

I'm planning to buy an Alienware 15 R3, the one with the 6820HK and the GTX 1070.

Regarding the DDR4 RAM memory, I can't decide between the 16GB 2667 and the 32GB 2400.

Anyone one knows the brands and models of each type?

What about latencies?

I tried contacting the online chat, but the salesman had no idea.

Thanks in advance!

Carmelo