I had a similar need to downconvert HPX500 720 p HD unedited straight from P2 cards to DV tape (don't ask why) in my car while driving cross country.
My solution was to use HVX200 to xfr HD to mini DV - it preserved the 16x9 and 24p
I think downconverted footage may look better than DV originated tape because of better lens on the 500 and shallow DOF that 200 would not provide.
I did what you suggested and rendered it. Looks like it worked fine. However the video doesn't play from the timeline through the firewire. I hear the audio but get a still frame on the monitor. If I start and stop the timeline the still jumps to the new location.