For me noise is an issue, it's not much better than the 1D II or the 7D. Also if you're looking at a 1D III make sure it's had the mirror issue fixed otherwise the focusing will be inaccurate. Personally I'd stick with the 7D, the extra reach is beneficial for nature and sports and I don't think the 1D III is a big enough upgrade (if you can't get something at 8fps you won't get it at 10fps but the weather sealing is better).
I had a 1D III for a few months and wasn't blown away by it at all - in fact I didn't really see a difference from my 1D II at the time.
I used to have a 1Ds III which I loved, simply amazing camera. Haven't used the 1D III, but I have rented the 1D IV a few times, and it was mind blowing, and the 1DX is supposed to be even better, damn. The 5DII simply sucks at anything fast paced, no matter what the fanboys say. So yeah, you'll love the 1D series, simply the best there is. Good luck
Just out of curiosity, why the disinterest in the 1ds mk iii? Extra 11 megapixels could be nice? That said, is the 1d mk iv too expensive or do you have another reason? Are you fairly set on 1D series?
The photog I assist has both a 5D mk II and a 1DS mk III. He's currently trying to sell off the IDS body because he just doesn’t use it any more. I could put you in touch with him if you like. I think he was asking $1800 the last time we spoke about it.