If your customer is willing to spend that kind of money, could I suggest waiting for Nehalem etc?
Then you could have:
Nehalem whatever CPU
Gigabyte X58 mobo
4GB DDR3
GTX280
I'd get one of the Antec Signature PSUs, though they may be a bit expensive, but I read a review a while back that found them to be flawless.
Antec P180 - I never suggest anything else.
But with these new processors, it may push th budget... Also depends if your customer is willing to wait.
he needs it this wknd