Its very hard to compare cameras for many reasons.
Even with the same lens the body/lens combo can be a bit out of spec with one and right on with the other.
for example, if you had a 1d3+70-200 2.8 and the AF was spot on and then you tried the same lens on a 7d and it was off by a bit it would appear that the 7d was not as nice but if you adjust the AF it COULD be just as good or better.
Add to that the massively different megapixel amount and sensor sizes and the 2 bodies are very difficult to compare.
I went back and forth for months about a 1d3 or 7d when I was upgrading from my year old 60d. I couldnt get my hands on the 1d3 to try but I did get my hands on 2 7ds that were very good.
So I bought the 7d and Im happy with it.
One thing to consider (and I think it was mentioned earlier) is the 1d3 does not do video where the 7d does. So, if you want to shoot a bit of video its not gonna happen with the 1d3 as far as I know.
I have only shot video once but it was cool. A killdeer was doing its "broken wing dance" which few people get to see. So I recorded it. Sometimes you take a tiny hit in one thing to pick up a bit somewhere else.
Here are a few shots with my 7d+100-400L combo (people say the 100-400 is not very sharp)
Many of them are 50% or more cropped too.
Loggerhead Shrike2 by jhayesvw, on Flickr
IMAGE LINK: http://www.flickr.com/photos/jhayesvw/8382922572/
Curved Billed Thrasher2 by jhayesvw, on Flickr
IMAGE LINK: http://www.flickr.com/photos/jhayesvw/8362876261/
Cactus Wren by jhayesvw, on Flickr
IMAGE LINK: http://www.flickr.com/photos/jhayesvw/8463182383/
Pintail Drake by jhayesvw, on Flickr
IMAGE LINK: http://www.flickr.com/photos/jhayesvw/8463189061/
Black Chinned Hummingbird? by jhayesvw, on Flickr
IMAGE LINK: http://www.flickr.com/photos/jhayesvw/8463189749/
Belted Kingfisher Flight 2 by jhayesvw, on Flickr