Play with other multipliers too. On the 920 and 1600 memory (3.6Ghz OC), my NB freq is showing 2800 and 720 on the memory. As a generic guideline, I'm also running the CPU at 1.28v, 180 bus, QPI at 3240MHz. I have the CPU multi to 21, but turboboost is off so it only runs at x20. By-21 only comes into play when in auto and TB is enabled. With a Manual overclock of all 4 physical cores...turboboost is not needed at all.
There's no reason we can't talk about water cooling in here at all. We can give good walk throughs too...wouldn't be the first time
I'd suggest a DIY loop that you can start small and build into for years to come. A good 1x120mm rad can handle a CPU and a single GPU just fine with 3/8" tubing. The temps you see with this basic loop should be equivalent to what you'd see with a single HS/F at stock speeds, yet you'll be cooling both parts in one shot/one fan and shoveling the heat right out of the back of the case. If there's even a slight chance you'll add more to the loop and your case can fit it, then
consider a 2x120 rad. The parts won't run cooler individually, but you'll have the capacity to cool the water more (that's all the rad does anyway).
More on that as it's often confused. The radiator just cools the water, the water transfers from the back side of the block. If you ever see a claim that CPU temps dropped by adding a larger rad, then the prior rad was under sized to begin with. An undersized rad leads to saturated water temps. Saturated water doesn't readily accept more heat. I ran a 1x120 for years (2004-2010) and never saw the water temp rise until very recently (i7, 470 GTX's...they just overpowered it finally and we had to part ways. Hear it has a good home though!). The block should move the same amount of heat to the water, the water will equalize the temp in the loop, if the flow remains the same.
I like 3/8" as the pump will make the water move faster through it than 1/2" tubing (again, given the pump's output remains the same). As it exits the tube and enters the block, the velocity gives a great cooling effect of it's own. A pump like Danger Den's CPx works great with 3/8" tubing where a big Laing D5 is best for 1/2".