Also can you tell us the timings of those memory sticks??
and the PSU isn't an overkill its a great PSU although I do recommend you get the 600w of that same model.
Also, yes I am also gonna advise you to go with E6600 over the E6700. theres absolutly no diffrence between the two.
Oh and that water cooling, dont get a prefab kit, get one from : www.petrastechshop.com
<<AWSOME prices, and AWSOME service!
Other than that, your setup is awsome[could replace the X1900XTX with an XT cus if you overclock you can get same speeds eventualy, buuuut an XTX is more convinient to some]