Choosing memory

Would it work if I used 2 DIMMs of 8GB of Corsair Vengeance LP + 2 DIMMs of 4GB *both 1866MHz* on the same mobo. I have only resorted to this option as i have am having trouble finding 2 DIMMs of 4GB in black, near to me, to go with my current 2 red especially at 1866MHz.

It's not ideal, but it will work. If each channel has the same amount of memory, then I don't really think it will be an issue.

Yeah it would have the 2 4GB DIMMs in 1 channel and the other 2 8GB DIMMs in the second channel, thanks.