what kinda overclock i should expect with this setup
Really depends on the CPU
With a good water cooling setup I think 5ghz should be pretty doable, any higher it will depend on your specific CPU
With water cooling your limit is not temperature, but the amount of volts it takes your cpu to reach certain clocks
No point in getting so much hdds lol, and two stock reference 670 gtx, when you can have 2000$ to spend get two good 670 GTX like the msi pe, the samsung 840 has tlc nand which is inferior to other ssds with mlc nand, with that money of the hdds i'd get another ssd or a 512GB one.
Like something like this : http://pcpartpicker.com/p/ByBG
Worth to mention it's already overkill.
The asrock z77 oc formula is excellent for extreme overclocking see here for some reviews :