Basic sensors effectively have one analogue to digital convertor (ADC) per column of pixels. That would mean that if you wanted to reduce the horizontal resolution, you would be disabling some ADC's, which in turn would reduce how many pixels can be converted per second, giving you no benefit.
You can do the opposite and increase horizonatal resolution for line scanner type of application with still impressive framerates:
"v2 camera can do 3280x32@720fps and 3280x64@500fps with frame skip rate less than 1% (tools attached)."
https://www.raspberrypi.org/forums/viewtopic.php?f=43&t=1091...
You can do quite impressive gobal external shutter capturings (with v1 camera only!), eg. capturing a 109m/s airgun pellet in flight on a single multiple exposure frame 10x: https://github.com/Hermann-SW/Raspberry_v1_camera_global_ext...
So for example, a sensor that 1920px × 1080px × 30fps has the ability to output 62,208,000 px/second - and with the same ADC and MIPI bus, halving the number of pixels can double the number of frames per second.
You'll note this article's demo, 640px × 65px × 660fps = 27,456,000 px/second. So you might plausibly get it a bit larger - maybe 640×120 - but you're not going to get HD resolution at this framerate using this hardware.
(Obviously, there's also questions like exposure time and light levels so it's not quite as simple as I just made it sound)