Hi, Paul and Doug.
First of all, I'd say that with either camera, you'll get great results, as long as you choose good lenses that meet your needs.
Six weeks ago I was in the same spot that you're in, trying to decide between the D70 and the 20D. I'd never had any Canon gear and my Nikon kit is all manual, with 200mm the longest lens, not good for birding.
Like you, I did my research, which was a bit challenging as all the Canon reviews were on the preliminary model. The D70 had a great track record and my D100 friends love their cameras. I love my FM3A, which is lightweight and straightforward to use. However, in the end I decided to buy the 20D, even though it was costlier. Some of the reasons:
8.2 MP provides a bit more image quality when you need to crop an image, which I frequently need to do with bird photos.
Initial reviews indicated that the 20D is a bit sturdier than the D70. Also it has some nice control features that I like, such as the thumb wheel and the small toggle. Overall, use seems a bit more intuitive.
Now, the big issue for me: the lenses. I reviewed and reviewed the listings of lenses made by Nikon and Canon. Overall, it seemed that Canon had more choices of lenses for birders who are "middle class" like me and probably can't afford to plop down $5000 to $7000 for a chunk of glass. In the $600 to $1500 range, there are a good number of prime and zoom lenses appropriate for wildlife photography, many of them image-stabilized, which I've found to be very helpful for birding as I often do it.
Given the costs involved in shifting to DSLR, I realized I could only afford one good lens at a time, so I decided that a 100-400mm or 80-400mm zoom would have to be the starting point, with eventual additions as I could afford them. Again, I looked at reviews that indicated that the Canon 100-400 was a bit sturdier and yielded slightly higher image quality than the Nikon. I think this was the clincher in making the Canon decision.
Another point - there are a lot more Canon birders, so advice on equipment issues is easier to come by.
Did I make the right decision? Well, I'm happy with the results I'm starting to get and know that as I learn to use the camera better, I'll improve. Would I have been as happy with the Nikon? Maybe....at least I wouldn't have been unhappy!
So that's a summary of my weeks of mulling over this decision.
Paul, I would recommend that you keep your 4500 for macro work, and then you can put off buying a macro lens until later. I had a 5000 that I've since passed on to my birding buddy, but I intend to borrow it now and then for close-up work. I found the macro image quality to be excellent and the camera is much lighter and easier to use than a large SLR, of course. You can keep it in your pocket without any inconvenience.
Best of luck to both of you in making your decisions.
Ingrid
