Jerkiness in turning is going to be relevant to your frame rate and the rolling shutter of the sensor, not your resolution. There won't be a change. ND filters may positively or negatively affect this "jerkiness" depending on what your desired outcome is.
Custom sharpness settings the same between tests?
2.7K is less resolution, less pixels, so it's going to look "less sharp" if comparing to a 4K source— but compared both at 2.7K they are identical in my tests at the same sharpness settings
What on earth? I just did a test and there is absolutely no FOV change when switching from UHD 4K 30 to 2.7K 30
Did you perhaps mean the switch from DCI 4K 30 to 2.7K 30? That is naturally going to happen because you're switching 190:1 ratio to the more standard 16:9