bdunbar79 does not having better AF and build / focus points, out weigh Iso issues? Im find my AF to be the hardest thing to deal with?
Please don't underestimate the power of the camera. I was just pointing out the negatives before you purchased this camera because no matter how good of a deal you have found, it is going to cost some money. The advantages of the 1Ds Mark III are that it has much better AF, better build, active-AF spot metering (very useful), and brilliant colors from ISO 50-200. The colors are something extra special and I can share some photos with you if you'd like. The saturated colors go very deep into the photo even in landscape shots, something you won't see with the 5D Mark II. Great camera.
The negatives I already touched on. In manual mode there is no auto ISO of course, it does not do well at higher ISO's (max 3200), and it has the DIGIC III processor.
The negatives may not be an issue for you. It does indeed depend on what you need the camera for. More lighting, yes get the 1Ds 3. If you're going to shoot weddings, don't get it. You'll have to make that decision. I too owned the 5D Mark II before the Mark III, so I know exactly what you are talking about.