at the f65 workshop i was at, a sony engineer claimed, and claimed very strong. 120 fps, in 4k. which just a loss in horizontal resolution, top and bottom. but it will still be 4k worth of resolution, with just an adjusted aspect. they will not be doing any windowing at all, or add any additional compression to achieve it.
and there is a 1080p mode just activated recently that records to SR codec, that is a full scale down. not sure about the FPS you can get on that, but there is no line skipping, windowing of the sensor of any kind. i'm sure it sacrifices a lot of higher framerates, but it's a complete down sample into 1080.
the way the sensor reads out is that it reads out from 4 quadrants independently reading that reading out the whole sensor, at once or one line at a time. so each quadrant literally has it's own set processing to get that info off fast, and all 4 pieces get re assembled when it hits the card. again, the camera really is no slouch. it's a fat camera, but it does produce a competitive image and quality. again, competition is a good thing, i'm sure Dragon is gonna be insane too. I hear Arri is coming out with a 4k cam soon, those are just rumors though but it's a inevitable thing. It's gonna be a very competitive era in digital acquisition.