saltedeggman, I've done lots of testing with lots of different waterblocks, cpus, and mobos. Here's my experience: You might see about a 5 degree difference from a good waterblock to a great waterblock, but that doesn't necessarily mean you'll increase your overclock much.
My general observations have been this. Going from high end air cooling (AX-7, SLK800/900) to good watercooling (maze2/3, spirals, db-2) will allow you to up the VCore and remain stable, leading to about 150-250MHz more clock speed.
Going from good watercooling to great watercooling (WW, Evo, Cascade) may yield you another 50-150 MHz increase. Until you go to extreme cooling (CPU temps below 0C) you won't see a huge increase in clock speed.
From looking at your system, I would say you will see the best "bang for your buck" by adding a shroud to your radiator, or possibly 2 in a push/pull configuration. Other than that, a Peltier may be your next best bet for a noticeable increase in CPU speed.