The EOS 5D Mark III is on the left, the EOS 1D X on the right. The Nikon V1 in the foreground is there to only provide a sense of scale. Although it does an excellent job for a camera of its size, have no doubt that Canon's cannons crush it when it comes to image quality.
By a fortuitous set of circumstances, Canon sent me their two best cameras, the EOS 5D Mark III and EOS 1D X, to use for a few weeks. It's been quite an experience.
Before I describe it, let me say that I have owned and used Canon cameras since the days of the Canon 7S rangefinder and continuing with practically every significant model they have introduced since. I had to slow my roll during the transition to digital, however. I simply couldn't afford to buy a new camera body every couple of years, especially since the full-frame 35mm versions were particularly pricey for an upper-middle income dad with a mortgage and three school-age children.
Even if I had the disposible income, my work is pretty much limited to street photography, travel, family, and portraiture these days. I don't need or want a full-sized pro camera, I prefer something small, lightweight, quiet, and unobtrusive.
These are not the first qualities that come to your mind when you think of the EOS 5D Mark III and 1D X. You think sturdy, fast, sophisticated, professional, and versatile. You think amazing image quality. You think, "I look serious as hell when I carry this thing around." If you actually are a pro on paid assignment--a wedding, advertising, or sports photographer for example--this is a good thing. For a street photographer like me, not so much.
Frankly, I've been amazed at how much attention I attract when I carry either of these rigs, especially the EOS 1D X. Typical comments (and my responses) include "Wow, that must be a really expensive camera!" (Compared to what?) "How much does it cost?" (You don't want to know.) "Are you a professional?" (Depends on what you mean by professional.) "How many frames-per-second can you shoot with that thing?" (Fourteen, if I'm not careful. But I'm always careful.) No one has asked if they shoot video. Perhaps that's simply taken for granted.
One fellow asked about the gadget I had mounted on the 5D Mark III's hot shoe. When I explained that it was the new GP-E2 GPS Receiver, he gave me a pitying look and told me that this feature was already built into his iPhone; plus, he could carry his iPhone in his pocket. I was suitably humbled.
As serious a commitment as it is to carry around equipment that's so large, heavy, and attracts so much attention, I discovered it takes just as much commitment to process the files. Raw files from the 22 megapixel EOS 5D Mk III average 30MB each. Each raw file takes approximately 15 seconds just to open in Lightroom on my aging iMac. I shoot JPEGs when I'm using the 18mp EOS 1D X in continuous mode, yet at 14 fps, even JPEGs can fill up a card pretty quickly. These are not cameras for people with underpowered computers and mere gigabytes of disk space. Terrabytes are the order of the day.
I will say this though: Looking at a 22MP file shot with one of Canon's best lenses, on a monitor set to 1:1, leaves no doubt about what you're paying for. The resolution, tonality, and subtlety of color are awesome. It's so easy to get lost in just how pretty the files look, even at high ISOs, that the need to also have an interesting subject to look at seems unfair.
If I were a fullt-time or even part-time professional photographer there is no question that I'd want an EOS 5D Mark III in my bag. (The speed, size, and expense of the 1D X would be overkill, at least for me. The same applies to the 36mp files of the Nikon D800.) I'm not a paid professional any more though, so even though I may miss many of the copious advantages of these luxury rigs, I will return them when asked and go back to the humble yet adequate equipment that suits me best. That, as far as I'm concerned, is the true luxury.