This is what I've tested so far

PowerBook 5300 results:
Booted with Apple's Mklinux booter, ended up as follows:

No filesystem could mount root, tried: ext3 ext2 ext4 iso9660 hfsplus hfs
Kernel panic - not syncing: VFS : Unable to mount root fs on unkown-block(1,0)
call trace:
[c381def0]-[c008cec] show_stack+0x70/0x1bc (unreliable)
[c381df30]-[c02083ec] panic+0x98/0x174
[c381df80]-[c0295e48] mount_block_root+0x2b0/0x2ec
[c381dfd0]-[c0296098] prepare_namespace+0x1a4/0x1e8
[c381dfe0]-[c029522c] kernel_init+0x10c/0x12c
[c381dff0]-[c0012130] kernek thread+0x4c/0x68
Rebooting in 180 seconds..

----------------------

PowerMac 5200:
BootX 1.2.1 custom / Mach Kernel.elf
BootX 1.2.1 custom / miboot.image
"wait some time" took 1-2 minutes

Apple Mk booter / Mach Kernel
BootX 1.1.3 / Mach Kernel.elf
"wait some time" took around 5-10 seconds

all of them ended up as follows:

wait some time
. . . . . . . .
Ready, reluanching kernel...
Preparing BAT...
id mach(): done
MMU:hw init
MMU: mapin
MMU: Set BAT for PowerBook / Performa
MMU: setio
MMU: exit


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