I’ve had the writer as slave. On both channels there were HDD masters. It happened regardless of which channel the data came from. That was on P3 550, 384MB.
Maybe the 7200A would like to go higher. But I’m okay even if it just reaches x6 (which I expect it to).
What speed did you get from the HDD(s), BTW? Curiously, under Win98, I can read faster from DVDs than from the HDDs. XP’s better in this regard, but closer to 20MB/sec rather than 30.