I don't know if this helps you, but I just made Digibeta dubs of my short film which was DVCProHD, 23.98, 16:9, 720p. My friend (who runs the post house where I did the dubs) recommended making an HDCam master, then just making Digibeta downconverts from that tape, just leaving FCP out of it completely. He wasn't happy with the results he got trying to deal with HD>SD, 23.98>29.97 direct from a FCP timeline, found this way to be much cleaner and less hassle.
HTH,
JK
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SCQT! Self-contained QuickTime ? pass it on!