Just make sure you check the video card carefully. I've seen prebuilt machines come with nice specs on everything, but a massively underpowered vid card for a machine being sold as a gaming rig. Check benchmarks too, video RAM isn't a good indicator anymore.

As for top of the line, while no price has been officially announced yet, it's general expected that Dell's super-top-of-the-line XPS-600 renegade with quad SLI is gonna cost $8-9000.