You have to be very careful when talking about DoF differences between crop and full frame. DoF is actually greater with larger sensors, so the 5D MkIII actually has more DoF than the 350D etc. However, when you start talking about the same field of view, then you will have less DoF on fulll frame, because you either have to stand closer or use a longer lens to get the same field of view. For me though, I took the step to full frame for landscapes and the differences in DoF never came into play, for the simple reason, I "see" differently when using full frame and simply frame differently. Of course, when it comes to wildlife and portraits, it would be a different story, as you probably would be looking for similar framing. In addition to that though, the effects of diffraction are less noticeable on full frame, because of the larger pixels and how they interact with physical characteristics introduced by lenses, so you are able to use narrower apertures with less softening due to diffraction. I believe the generally accepted differences in DoF when using the same field of view is around 1 stop, which is made up for (and probably more so, based on my anecdotal experience, not measured scientifically) by the differences in the diffraction limited aperture between full frame and crop sensors.Congratulations and welcome to CR! That having been said, look forward to you posting pictures!
BTW, I went from 300D to 5D3 and so I understand your delight! One word of caution - the DOF is very different. It takes a while to fully comprehend that... Also don't hesitate to push the ISO. It is not grainy at 800 I had a hard stop at 400 ISO. With the 5D3 even 12800 and 25600 ISO can be workable!
One more thing - if you think the images are soft even when you take a stationary subject from a tripod, try live view focus. If that is sharp and the normal AF is soft, you need to micro-adjust the AF for your lens.
Define very different. I heard through the grapevine that full frame cameras are a 1/2 stop shallower in depth of field than crop sensors at the same aperture an focal length. Is the 1/2 stop that substantial of a change?
I have enough to get an mkiii... but I don't want to be impatient and buy one only to find that I could have saved an extra $200 in a month. It's a quandary.
I'm going to have to re-read this when I'm not tired. Thanks for responding...