Thank you everyone for the responses, very much appreciated.
My main reason for shooting 3.2K or UHD is the (slightly) larger sensor area used and the ensuing larger angle of view. Also, through my experience with originating in 4K (on different cameras) and downscaling to 2K, I've noticed a slightly sharper image than a 2K origination, which I normally like.
As David said, I was indeed wondering about the scaling pre-ProRes, and whether it mattered. But tests are definitely in order.