To your question about duel loops.
In this configuration you are running 2 pumps 2 rads. One loop for the CPU and mother board in my case and a second loop just for the VGA. Keeps things quiet and cool!!
With this in mind is your customer overclocking the computer or just looking bragging rights? Water cooling is not cheap!!!! I probably have $800.00 vested in mine but I have overclocked the crap out of mine. Have a i7 950 running at 4.5 mhz 40 c average start up temp running prim will get into the mid 70's. SLI 570 gtx overclocked holding around 34 c after a 3DMark test.