Many of us use both crop and full frame Canon rigs. Interestingly, when we wring our hands about these feature lists, that sensor size enormously effects the relative benefit/curse of the upgraded features. There are diminishing rates of return that start to come into play, particularly with the 7 series' crop sensor size.
The basic compromise AHSanford correctly sets out is the megapixels versus frame rate question. (Plainly it's not just a simple calculation of available throughput. Canon is perfectly happy underwhelming its cpu and cache by downplaying fps just because, such as in the 5D4.) Here are the two points I wanted to make:
ON RESOLUTION:
I do a lot of cropping with wildlife shooting. I'm more often than not at 1:1 magnification in Lightroom, estimating whether or not the medium in which the shot is going to be published will make the relatively low resolution output I'm about to export look like crud. So it was magical when the 5D4 came out with the unexpectedly large megapixel boost to 30. It went half-way to making the full frame sensor perform like a crop for the purposes of magnification. And I know, from having borrowed the 5DSR, that it could go to 50 and not break up.
This cannot happen on crop with current technology. Things get very muddy now at the 20 megapixels as it is, in good part because the crop sensor size makes the pixels very small, and we're taunting physical limits. I do hope that Canon can expand that ceiling using some the tech they've recently introduced, like on-chip ADCs, etc. But going from 20 to 28 megapixels will give significantly less benefit than seen on the full frame sensor.
I want the extra stop of shadow drawing that I get with the 5D4 files. So if Canon uses the new tech to have a 1.5 stop advantage, I'd rather than put only a small portion of that against allowing an increase in resolution, but the brunt of it against giving more dynamic range and file malleability. Going from 20 to 24 mp seems small, but it's a 30.5 percent decrease in pixel surface area. Put another way, if 10 photons were going to hit that pixel, now it would only see 7. This is why having a 5D4 that got boosted to 40mp would have been a fine idea, and a 7D3 that got boosted to 28 would have been wasting image quality on more pixels.
THE THREE LIMITATIONS OF FPS:
1) This will sound crazy, but there is such a thing as too many frames per second in a situation. Generally, people who are fans of mashing shutter buttons to get long strings of shots separated by mere milliseconds do this only in specific circumstances. And in those circumstances, 50 frames per second wouldn't be too much, buffer willing. But most times a 10-12 fps rate is more than adequate, or at least a compromise with our future selves later at night culling through the 95 percent of the shots we're going to throw away. This issue of too many FPS or too few, depending on the situation, is solved with a variable shutter button. Don't give me a menu option to change fps. People who vary fps don't have time for menus between shot recognition and click. The shutter depress needs to be graduated. We're using back-button focus anyway, so the "half press" should be dedicated to a modulated frame rate.
2) As a group, we often have underestimated the benefits of more frames per second in the past. Back when we thought 7 was high, 16 sounded stupid. The current 7D2's 10 is pretty good, but you'll notice more keepers (and even more non-keepers) if you shoot a 1 series with the higher fps. Having moved up and down in this fps continuum, I see a diminishing rate of returns somewhere between 12 and 16 fps. This is an interesting number because the industry has sort of arrived here, which means soon it will not be a good distinguishing factor between camera lines such as the 7 series versus the 1 series. Just in time for mirrorless to take away the limitations of the mirror mechanism. Sure, mirrorless will give us 40 fps, but at that point, it's just video, and Canon's motion JPEG format starts to seem prescient.
However, now that we're at this upper limit of utility, I think we tend to overestimate the value of more frames per second. To put it simply: if I were offered the same camera at 7 fps versus one at 8 fps, I'd sacrifice a lot to get the extra frame. I'd pay 15-20 percent more. If I were offered a 15 versus a 16 fps camera in different colors, my color preference would be more important. And I don't really give a damn about camera colors. What would make me buy a different camera is the buffer size - something that never makes the spec lists prior to launch, which has always been a mystery to me.
UPSHOT:
Give us 24mp, 15 fps, 1 stop of extra (ISO performance +/or file malleability +/or dynamic range) geared to the high end of the ISOs, which is where 7D2 shooters are pegged.
