With those specs, games won't take use of it yet to be honest.
That setup would be more useful for editing/rendering/music making applications that may use more of it.
If you are building that rig for gaming purposes only, its a complete waste, but for other uses, in the next few years, you may be able to use alot of it with updated programs, etc.
New graphics cards are coming out now that are more energy efficent, but more powerful than the last generation, so may be worth looking into instead if you can afford it (No doubts there
Don't bother with buying seperate Ageia Physx cards though, but yeah, the Nvidia cards do have the function now, and will be used for physics/other applications.