Just had a better look at mufastrom. It doesn't seem to take down my CF speed as seriously as I first thought.
The speed of my CF card is a little slower, but overall system speed is a little faster.
HOWEVER, the gurus still happen when I use mufastrom.
So, both with cpu fastrom and mufastrom I get gurus. All the same guru : 8000000b line 1111 emulator error.
This even happens with normal copy/delete operations.
If I don't use a kickstart remapper tool all is fine.
Under WB3.1 it also doesn't happen. Just checked my 3.1 guruhistory.dat file.
Didn't have a guru in the past month. That is until I installed os3.9.
I don't want to go back to 3.1, so I just won't use a kickstart remapper.