As far as i'm aware it's very dependant on what player is doing the conversion process to how good the quality is.
My Denon 2900 doesn't really do a conversion, it leaves the picture squashed(525 lines onto 625) and juddery(PAL50). But my old Pioneer 717 converted to PAL60 which left you with a more than appectable picture.
I'm not sure how the DV-89 copes in this area, is it an Arcam model??
Interesting what you say about the DEnon 2900, I saw on a progressive scan evaluation site (don't remember which now) that it was supposed to be quite good in this area.
The denon conversion that you refer to, is it only in Interlaced mode, or are you talking about progressive scan??