Upload & Sell: Off
I'll add one more lens for you to consider: The 70-200mm f2.8L (non-IS).
If you are primarily interested in "street photography, nature and maybe some outdoor sports" I don't see the value of going for an IS lens. Assuming you are shooting in daylight most of the time, the IS won't make a huge difference in street candids or nature shots, and the non-panning type of IS is of no value to sports photography.
If you're thinking, as you say, of going with a lower-end, refurbished body in order to buy the 70-200 mark II, you might want to consider instead going with a 5D2 and the 70-200mm f2.8 non-IS instead. I've seen a couple for sale used on the Buy/Sell boards for under $1,000.
As far as sharpness comparisons go, wide open at 200mm, the 2.8 non-IS seems to beat the 2.8 mark I:
Meanwhile, the 4.0 IS seems better than the 2.8 non-IS:
And the 4.0 IS seems pretty close, even, to the 2.8 mark II :
The 2.8 mkII is the hands-down winner in terms of optical quality across the entire frame but the question is whether it's worth sacrificing the image quality of your camera body in order to get that lens. I think a 4.0 IS with a 5D2 might be a better fit for you, in terms of sharpness and bang for your buck.
Personally, though, I would feel a bit limited with the f4.0 max aperture. I was in the same boat as you a while back (trying to decide which 70-200 to get) and ultimately went with the 2.8 non-IS because I wanted the faster glass at a reasonable price. Initially that was more for indoor sports but I found I liked the wide aperture for portrait-style animal photography, as well. These were all shot at 2.8:
Just one other thing to consider. Good luck with your decision!