Comparing a vastly different $3,300US 5D to a $1,700US D200 camera is rather difficult. If I were paying twice the price for a camera, I would expect it to have more than a slight edge over the camera half its value. The Canon 5D has only 25% more pixels - not really enough to be noticable in a print.
Canon 5D - 4368 x 2912 - 14.5" x 9.7" @300dpi Nikon D200 - 3872 x 2592 - 12.9" x 8.64" @300dpi
Considering the cost of the 5D is double that of the D200, the difference is insignificant. What counts more is how sharp and clean the result may be. Both could be blown to enormous size and given comparable lenses would produce outstanding results.
The 5D sits between the D200 and D2X in price, and there is not really anything in the Nikon lineup to compare it to. The D2H is a sports/journalism camera and very specialized. It sits opposite the Canon 1D and neither have the least bit in common with either the 5D or the D2X.
The Nikon D200 seems more in the class of the 20D, and seems to come off favorably. The 20D has been on the shelves now for more than a year, and has dropped significantly in price to about $100US less than the D200. Since we seem to be counting pixels, it is 8.2MP 3504 x 2336 - 11.68" x 7.8" @300dpi - slightly less. I expect it will be replaced shortly. While Nikon has kept the D100 in production since shortly after it was announced in February 2002, Canon seems to croak their models much quicker.
The real test will be of the D200 vs whatever Canon comes up with next in that specific range. The D50 and D70 as well as the Canon Rebel models, are clearly entry-level cameras. The D200 and 20D are clearly prosumer, while the FujiFilm S3 and 5D are entry-level pro cameras. Early reports on the D200 with preproduction s&les indicate that it has much more in common with the D2X than with the D70.
Realize that these are digital devices with added lenses, and Moore's Law impacts them. The FujiFilm S3 was announced at PMA in February 2004, and while it was a topnotch camera then, the D2000 likely will surpass it when it ships. The Fuji is priced opposite the 5D and uses all of Nikon's DX lenses. Most of the lenses for the 5D were designed for film.
Who knows what is best for you? One can read specs until your eyes pop out, without really learning much. What really counts is how the camera meets your needs. Does it feel right in your hands? Does the operating system controls and menus help you or hinder you? Do your present lenses work with it? Does the cropping factor nullify their purpose? If you have to replace your present lenses, are there lenses designed for use with sensors that fit your way of working? Are there features that will advance your photography, or is the camera really designed for someone else? Do you have the skills to get the most out of it? Would you be better off with a 21st century mirrorless design, rather than a mid-20th century SLR design with a sensor and digital electronics grafted in?
Only when you can get your hands on the actual cameras, can you really begin to judge. S&les from pre-production cameras on review web-sites, may tell more about the reviewer than the camera. I would not think of advising in this case, not having shot with the 5D and with the D200 perhaps months away from being on the shelves.
What other cameras will exist when it ships? There are two still-secret models about to surface from Nikon that I have caught my intense interest for ex&le, but by the time they hit the shelves, there may well be competitive models from at least two or three other companies. Even though they sound like they would deal with the only complaint I have with my current kit, I would still want to see what the competitors are bringing to market. They should be announced sometime between now and PMA in February. I have used a lot of Nikon equipment over the years, but many other brands as well. What counts is how the device improves my images - not who makes it. I am in no hurry.
I don't like to be a beta tester on my own dollar. Here in Western Canada, it is said you could tell the pioneers by the arrows in their backs. Testing by company technicians in a camera R&D lab is vastly different from a photographer shooting in the field. I am very happy that all the companies do offer firmware upgrades, but I would rather buy with the first one installed. I have an aversion to version 1.0 of anything.
As a horrid ex&le, when Kodak finally brought their 14n to market a couple of years back, there were firmware upgrades every week or so, and they never did properly finish it. Eventually, they brought out a new model and made a trade-in offer that pretty much amounted to buying the old clunkers back.
The pioneers - early adopters who put their deposits down ages before the camera eventually shipped - found an unfinished camera that eventually only worked well within a highly specific set of conditions and worked very badly with many fine Nikon lenses designed for film photography. Since it was a full-frame sensor, Nikon's excellent DX lenses did not have the coverage to work with it. Buyers were stuck with film-designed lenses. Even worse were Contax owners with deposits, waiting for the 7D with their pricey Zeiss glass. Years passed, and the shipping date was perpetually delayed. I understand a few were finally sold in Europe, but the whole thing was a disaster. Such a disaster, that Kyocera has disbanded Contax in retailation.
I also would not venture an opinion, since it would be the wrong camera for me. After shooting hundreds of thousands of exposures with SLRs, and finally reaching the point where once again I can shoot for me - and not The Man, My Nikon F3 system and Bronica ETR system have not captured a single image this century. When I shoot film, it tends to be with medium-format rangefinder cameras, and all my digital work is with mirrorless contemporary designs. If someone made me an offer I could not refuse, I would again shoot with the ancient SLR designs, but only if the money made the trade-offs worthwhile. I may never shoot another image with an SLR during the rest of my life.