Not sure what you need 8GB of memory for, but try two sticks in the outside slots first. You will need to increase your FSB frequency. From there your CPU will start to overclock, and you should see different options for RAM frequency. You may need to switch your RAM settings to Manual in BIOS if you haven't done that already.
Make sure timings and DRAM voltage are set to run 1600 b4 you actually start the OC. As a nice mild overclock that shouldn't be too hard to achieve, I would work my way up in 50MHz increments to 400MHz. That will give you 3.4GHz on the CPU at max multi and a nice even divider for the RAM to run at 1600MHz. Not sure how your BIOS works, but mine gives options for RAM frequencies based on what FSB I have chosen.
You will need to add a little CPU and northbridge Voltage to run that overclock stable.
As an example, I have that CPU on a GA-X48 board. For 8.5x450FSB = 3825MHz , I have my Vcore at 1.35v, and the NB voltage up a couple of notches since the FSB is now running at 1800MHz. The FSB VTT is up ~1.3v and my GTLREFs are set to -40mv.
You shouldn't need as much voltage increase or tweaking of auxiliary settings to reach the 3.4GHz I mentioned above though.