I think it's going to be very similar to what the 1D MKIV can offer but the battery life can't possibly be even close to what the 1D MKIV can offer.
I can't imagine the image quality is going to be bad at ISO 4000-6000. I'd say it's probably going to be right up there with the 1D MKIV. I'm also curious about how well this camera will track and focus for sports situations.
It's definitely going to be a tough decision but it's also going to be extremely hard to pry this 1D MKIV away from my hands. Once I see more field tested reviews then maybe I will consider it.