"I am aware, from reading previous discussions here, that the crop factor is not a huge advantage (if at all),"
Dan, if the 1.6 factor helps you to fill the frame and you can't otherwise, then it is an advantage that you can't make up by cropping FF. I believe jrista has explained this in other threads. The huge downside of crop is the smaller pixels that result in poor high-ISO performance. If you have 24 MP in a crop, the resolution should be pretty impressive, assuming top of the line lenses (advantage goes away as FF gets more MP).
I read jrista's comments about it a while ago, and to be honest I had a conclusion in my mind that, in the end, one could achieve similar results when cropping FF. Have I misunderstood? Maybe it was exactly that, pixel density was counterbalanced by cleaner image, and in the end there was no clear advantage for crop. I am not sure anymore, though, and if you are, well, I guess I had better believe you...
Question: Is it better to shoot with a crop camera than with a FF + teleconverter?
Anyway, other than that, I am not sure it will be worth buying a 7D2 because a 5D3 will be costing (am I wrong?) nearly the same at the time. We keep praying for 5D3-like AF, 5D3-like IQ etc... Well, if the price is similar, then I see no advantage of the new 7D2 except for when the extra reach is important (not my case).
(Sorry if it was waaaay off-topic.)
Thank you for answering, Jack!
The quirky thing about that question is it has changed over time. Back when the 7D was first released, there was no question it produced better results in reach-limited scenarios. It's higher spatial resolution extracted more detail, even if that detail was a little more noisy.
The situation has changed today, with the 5D III and 1D X. Both of those cameras have considerably less noise than the 5D II did beforehand, and even less than the 1D III and 1D IV. The quirk here, is that with so much less noise, the detail they resolve can be pushed around more, and cropping then enlarging still produces great results.
Now, technically speaking, the 7D still resolves more detail. The 7D has 4.3 micron pixels, while the 5D III has 6.25 micron pixels. You can fit 2.11 7D pixels into every 5D III pixel. Even despite the AA filter and the noise levels, the 7D still resolves more detail. I think the key difference most people observe is that the 5D III images are crisper and smoother and cleaner, which in the grand scheme of things produces more pleasing results.
I feel it these days, when I take nice, razor-sharp images with my 7D, they still lack the clarity and cleanliness of similar 5D III or 1D X images. For those who shoot with the 5D III or 1D X with a 600/4 + 2x TC, even though they have a smaller maximum aperture, their results are STILL less noisy than what I get with my 7D. The 7D only gathers less than 21000e- per pixel at maximum signal (and most images don't expose every pixel to maximum, so the average signal in terms of charge is probably less than 18000e- at ISO 100, and certainly less than that at higher ISOs. The 5D III has over 67000e- per pixel at maximum signal, and the 1D X has over 90000e- per pixel!! The 1D X has a stronger signal at ISO 400 than the 7D does at ISO 100. The 5D III has nearly as strong a signal at ISO 400 as the 7D does at ISO 100. It's that stronger signal that largely overpowers the loss in resolution. For what detail those two cameras DO resolve, despite being less detail than the 7D, it is more well defined detail.
If the 7D II gets its much-needed sensor improvement, and achieves around 30000e- FWC at ISO 100, then that would bring it up to par with the 5D III at ISO 200. That's a full stop of real-world improvement. That could have significant implications for the 7D II IQ. Especially if it achieves that increase along with a resolution increase. At 24mp, with 30000e- FWC, the 7D II would once again be able to offer a TRUE reach advantage over the 5D III and 1D X. It would be roughly equivalent to using the 5D III or 1D X with 1.4x teleconverters to achieve more reach, which would level out the noise differences...however the 7D II would still have a meaningful resolution advantage. Both FF cameras could still be used with 2x teleconverters, at which point they could regain a small advantage over such a hypothetical 7D II...being able to pack more pixels on subject with only slightly greater noise.
I dunno if that answers your question or not, but there is a bit of generational flipflop going on. The 7D used to demonstrate a significant resolution advantage over FF models. With the 5D III and even the 1D X, that resolution advantage is no longer sufficient to overcome the benefit of having less noise with FF. With the 7D II, assuming it gets all the goodies we hope it does, it will once again attain that resolution advantage. If that occurs, then there will be no way to get around the fact that as 7D II with 400mm lens will be just as good as a 5D III with 600mm lens, for a very small fraction of the cost.
(Can't forget the very significant cost advantage that the 7D enjoyed for so long...the 7D II will have it, too!)