So what crops are we talking about with these resolutions?
For now, you have two options that works reasonably well with 5D2.. I can describe it in a few words.
First option - to record using full sensor, so you will get the full-frame look. The resolution in this mode is 1880 in width, so it is slightly less than 1920, but it is not a problem at all, and most older cameras don't shoot really in 1920 natively, sometimes they do much larger upscale, you won't even notice this small 40px upscale.
You can shoot up to 30/31 fps with this mode, and there is another preset for slo-mo, where you can shoot using 48 fps, but the resolution will be limited in height, 1880x744. which is still cool and cinematic. And it is RAW, so it upscales really good.
This mode is called 3x3 and although it uses the full-frame, it has some drawbacks. To read the full sensor area, it uses pixel binning and line skipping, and it produces aliasing. Sometimes it is very noticeble, sometimes not. This is the reason why many people prefer vintage lens and shoot wide open, it helps a lot with aliasing. Native h.264 (.mov files) from camera uses this mode also.
And there is another option - shoot 1:1 in a crop mode. It doesn't skip any pixels, so there is no aliasing, but the camera is too slow to record the whole 5.6k sensor at 24 fps, so there is a preset 2784x1160 24fps, and you can upcsale it to 4k or downscale to 1080p, and it will look great.
BUT. It will use only center of the sensor, so you will get a crop. And it is about 2x crop. The sensor is 5,6k and you recording only 2,7k. So you will probably need some wide-angle lens because of that 2x crop. And this mode is only 24fps, and you also need a very fast CF card for this, the file sizes are bigger, and you need faster PC to process them. And this mode is less stable, you can get crashes sometimes.
There are some other modes but they are even less stable. And there is also 5632x3124 @ 3.8fps which uses almost the whole sensor, and it looks absolutely fantastic, but it eats cardspace like crazy
What can I say about the quality... I had sony a-37, and the difference is night and day. RAW video is fantastic, it can look like a photo. But you'll have to learn how to use it properly, and it takes A LOT MORE TIME to shoot and process raw clips. I warned you!
5D2 also doesn't have any image stabilization! It could be difficult to shoot handheld after Sony.
And if you have money for 5D3, definitely go for 5D3.
Personally I mostly use 3x3 mode, it's just more convenient and simple to use, and my CF card is not that big and fast... And to fight aliasing I use vintage lenses wide open. And they vignettes a lot, have distorted edges... So it is very vintage look, but you can color-grade it very deeply, push the shadows a lot, and so on. Sometimes there is still too much aliasing, so I discard some footage sometimes..
I think you just have to embrace it as it is, no 4k but who needs that 4k anyway? It's RAW and it's awesome. I really enjoy this whole process of filming with raw, although processing it and stabilizing everything in post takes ages on my old laptop. But it's so cool anyway, I'm just really happy with it
