Right out of the gate let's just say that for overclocking the memory above 1600mhz the return for the judicious amount of time you will spend configuring and testing, and retesting, and reconfiguring, and tweaking and tuning the speed and timings and voltage, the gains are not worth it unless you are simply trying to achieve higher benchmark scores. In real world usage, it's doubtful you'll see any meaningful difference by jumping to 1866mhz or by tightening up the timings. Just stick to the XMP profile unless you simply want something to do with your time, in which case, by all means, spend countless hours fiddling with your memory configuration like many of us have done just to find that it really made very little difference in the long run.
If you want to do that, I can certainly point you down the path, but there's a lot more to be gained by focusing on the CPU configuration than there is bothering with the memory. Plus, with that much installed memory it's VERY IMPROBABLE you'd ever find a stable configuration past the basic XMP configuration anyhow. I'm actually rather surprised that you're even stable at 1600mhz, if those sticks are all part of a 1600mhz kit, with what I'd assume must be eight sticks.
As for the CPU overclock, there may be some room there for gains. Much, maybe MOST, depends on the motherboard model, CPU cooler model and whether there is sufficient case airflow in regard to both intake and exhaust fans. If you don't have at least two front intake fans of 120mm or larger diameter, and two exhaust fans (Usually one rear and one top rear, or one rear and two top), then it's probably not even worth your time to attempt unless you're willing to invest the money necessary to ensure sufficient cooling not only of the CPU but through the case to help keep the motherboard voltage regulation components cool as well. Considering you have water cooling, some of the preferred requirements for the case fans will likely be absorbed into the presence of the radiator, which will take the place of some of the case fan requirements.
Knowing your exact motherboard model, exactly how many case fans, where they are, what size and models they are and the exact model of your water cooler would be very helpful in even trying to determine whether or not your system might be a good candidate for overclocking or not, or what would be recommended to add in order to try.
Also, "vented" doesn't mean much in this application. Active cooling is necessary for adequate cooling when overclocking. Venting is not generally a sufficient configuration depending on what is meant by that.