3. Yes a new and better body than the 7D would help, but unfortunately Canon isn't giving much to choose from.
My argument was that no-one seems to offer crop cameras with "significantly" better high-ISO performance than the 2009-vintage 7D. Everyone claims to do so, but when you look into the marketing, it tends to revolve around out-of-camera jpeg only (i.e. improved in-camera noise reduction) that should not matter to raw-shooters. Improving hardware (i.e. raw) performance at high ISO seems to be a lot harder.
Attached is a list of what I would consider top tier high ISO performers. As you might guess, they are all Full Frame and the only Canon on the list is the 1Dx at the bottom.
Comparing systems of different sensor sizes is kind of mind-boggling, and the claimed "big-sensor-advantage" may or may not be relevant to real-world snapping where you have to pay for and carry your lenses, and where you might have constraints on DOF.
Both the 7D and 7DII are marginally outperformed by my D7100! A list of APS-C cameras is attached and again dominated by Nikon. (Note lists are only Nikon and Canon).
The top crop performer according to dxolabs is the Nikon D5500 (ISO1438), while the Canon 7DII gets (ISO1082) and the 7D gets (ISO854).
If you look a bit closer at the graphs for SNR18% and (in particular) DR downscaled to 8MP, you'll see that the single "low-ISO" rating removes a lot of information about the sensors. The single most distinguishing feature of Canon sensors vs all others is the lack of DR at _low_ ISO (ISO800 and below). At high ISO, the 7DII seems to be at least on par with the D5500. The 7Dmk1 lags slightly behind (0.75 stop or something)
http://www.dxomark.com/Cameras/Compare/Side-by-side/Nikon-D5500-versus-Canon-EOS-7D-Mark-II-versus-Canon-EOS-7D___998_977_619Let us add some visuals (since this is a photography forum, afterall). The dxo rating seems to suggest that the Nikon camera has "tolerable" quality up to ISO1438, while the 7D does to ISO854. So at (manufacturer rated) ISO of 1600, the Nikon must beat the 6 years old 7D hands-down?
http://www.dpreview.com/reviews/nikon-d5500/8I don't think that it does. In my view, the noise appears quite similar in that test, although the Nikon does seem to have slightly more detail. If I was to do low-light sports, I would be a lot more concerned about affording, supporting (and carrying) the right lenses, and getting focus right than these sensor differences.
-h