The only questioon I would have is how does the compressed HD compressed to MPEG-2 (the DVD format) compare to uncompressed SD compressed to MPEG-2. My guess is that differences, if any, would be trivial. But with all the juice you're putting into this it might be worth a look.
We just did S16 --> uncompressed SD --> DVD and it looked mighty fine. Don't forget to make your DVD anamophic!
-D