Can anybody chime in regarding the resolution limit (640x64) -- If this is for memory reasons, could we pick alternate values such as 200x200 as long as the total pixel count is the same?
This is normal for high refresh rate cameras. They store straight to ram then dump to the disk (SSD) after. Especially the higher end cameras, they literally can't store data fast enough to go anywhere else.
Light exposure on the sensor, the faster the frame rate, the darker the image as its a fixed aperture. Photographic buffs could explain it better, but my take is the faster the exposure the bigger the aperture that is needed to let more light in to make the photo look well lit. I don't know if parts of the sensor also work faster due to its circuit design but I would imagine this is also a factor just like its possible to read more data form the outside of a spin disk than the tracks close to the centre.