Actually that's quite inaccurate. Most of the time, on 2-4 rail PSUs, a single +12V rail is running more than its "fair share". They're also setup so that high-end setups are balanced--by putting different graphics cards on different rails, they can run more cards. And actually, higher-quality PSUs are typically not triple or quad+ rail. They're usually dual-rail. That gives a nice balance between CPU and PSU. Anyways--any half-decent unit will be have a nice peak output and will be rated by sustainable max output at whatever temperature they determine (40C typically).