In choosing between the 5D and the D2x, there are a lot of issues, but disposing of your present Canon stuff to switch to Nikon would cost you a lot without necessarily gaining much...The fact is, the image quality of the 1DSII and the D2X (and probably the 5D) are so close as to make "quality" of final print more of a question of technique than of camera. Some points:
You mention that the D2X feels heavy. The 5D is lighter, at about 2 pounds compared to about 2 pounds, 8 ounces for the D2X. The 1DSII is a real brick, coming in at 3 pounds, 5 ounces. (There's a bigger weight difference between the 1DSII and the D2x than between the D2x and the 5D.) The D2X really isn't a heavy camera. But you have to understand that the quality of the cameras is different -- the D2x and the 1DSII are fully professional cameras with stuff like weather sealing, better autofocus, etc.
You talk about looking for a solid wide angle lens. If your main use is wide angle, I would check carefully the corner softness of the 5D (and the 1DSII for that matter.) Nikon's WA lenses are better. But: Canon-mounts take other brands of lenses, and I am told (on this forum, somewhere) that WA Zeiss and Contax lenses work well on Canons, with readily available adapters. It would cost you a few bucks, and you might want to explore the issue with some other Canon shooters (I shoot a D2x), but that may be a solution. If the 5D comes in at the $3300 price, you could get a #### good WA lens for the difference between $3300 and $4700 of the Nikon, and not have to give up your other Canon equipment.
In my opinion, contra Michael's, full-frame is essentially a non-issue; if anything, I think, like Bernard, that the benefits of a smaller sensor outweigh the benefits of full-frame, as long as final print quality is essentially the same.
But the cameras are different in ways other than sensor size. Canons apparently are better in dim light, which is a benefit for fast-action sports shooters working in arenas or other night-time or dimly lit venues. The only time I personally have shot anything faster than ASA400 is the occasional through-the-glass-in-the-museum photo, where you can't use a flash because of reflections, and tripods are not allowed. Basically, the quality of shots of ASA1600-3200 are another non-issue for me, but it may be an issue for you.
There is also the question of ergonomics. Ergonomics count for me, but the slower you work, the less important it is, IMHO. If you have to work fast, as in street photography or news photography, it can be pretty important. On the other hand, you can get used to almost anything, with time. News photogaphers (Weegee) used to do grab shots with Speed Graphics and flash bulbs...
JC
