I think that the only way to make this decision is to perform a test of each workflow.
You'll want to test two scenarios:
1. Record 2k vs. record UHD with no cropping or repositions
2. with repositions and with zooming in as this sometimes occurs.
then see if you can see any practical difference. I suspect that it might be difficult to see any meaningful differences, but who knows?
Also, keep in mind that when shooting at 24fps maybe one out of 36 frames will be free of significant motion blur. So very few frames actually have 2k, 3.2k or even 4k resolution. Of course, static shots without movement will show the maximum resolution possible.
So, when you test, don't just shoot static test frames. Also shoot something with pans, camera moves and subject movement to really get an idea of the differences in the capture workflows.
In reality, if you don't have access to the camera and post facilities to conduct the test, you'll always have a sense of doubt about choosing to record 2k, and I suspect that you'll choose to capture in UHD, with the additional expense of doubling the hard drives you'll need for capture and back-ups. And, perhaps, you'll also need the additional step of transcoding everything to 2k or HD for editorial as well.