Well, I will use my system as an example. This is in no way a direct comparison to your system I am just trying to give you an idea of what water cooling does for a similar system (component wise). Sorry, I had to put that in there because someone would read this and say..."temps are irrelevant and you can't compare systems no matter how similar they are...there are too many variables".
With that said, here are the types of temps I see. I have a full size ATX case (CM stacker) and both my x1900xt and 640 (4ghz/1.5v) are included in my water cooling loop. I have two 120mm intake fans, one 120mm exhaust fan, one 80mm top exhaust, and 2 120mm fans on my BIX II. All 120mm fans,38mm thick, are Sanyo Denki's and run at 7v on my sunbeam rheobus. The 80mm fan runs directly off of my PSU @ 12v. I an apogee on my CPU and a maze 4 on my GPU (copper ram sinks on ram). In the morning my ambient temps are around 25c. I get idle temps of 29c(CPU) and load temps of 35-36c(CPU). As the day goes on my ambient temps go up to 31-32c. I get idle temps of 35-36c(CPU) and load temps of 43-44c(CPU). I have seen ambient temps as high as 34c and load temps as high as ~50c. My video card pretty much idles at 40c(2D mode) and loads at 51c(3D mode).
As you can see we are talking about a serious amount of heat here.