To sort of answer my own question, I found some discussion an it was
mentioned that QEMU is faster so it's likely what should be used. One
person mentioned using this with QEMU:
qemu-system-ppc \
-boot c \
-M mac99,via=pmu \
-m 512M \
-cpu G3 \
-prom-env 'auto-boot?=true' \
-prom-env 'vga-ndrv?=true' \
-drive file="macos_921_ppc.iso",\
format=raw,index=2,media=cdrom \
-drive file="MacOS_9.qcow2",\
format=qcow2,index=0,media=disk \
-name "Mac OS 9.2.1" \
-netdev user,id=mynet0 \
-device sungem,netdev=mynet0 \
-no-reboot