I flashed the card with the reduced R127 ROM from the macelite downloads.
Device ID 5961 is a 9200SE, which is very similar to the 9250. This is why I chose to replace that one. Plenty of other choices but this seemed to be the closest match from a hardware point of view.

In the meanwhile I put up the whole set of extensions I have installed to get accelerated video here if someone wants to play with it: http://macintoshgarden.org/apps/ati-radeon-9250-mac-os-9-drivers