What mobo - sounds like a 3 slot which is normally an X58 - if so the slot closest to the CPU is generally the lead slot and with 2 sticks to be able to enable dual channel then you want 1-2 from the CPU
What mobo - sounds like a 3 slot which is normally an X58 - if so the slot closest to the CPU is generally the lead slot and with 2 sticks to be able to enable dual channel then you want 1-2 from the CPU