4MB of fastram is not too much to play doom. You should try configuring your card with 8MB as there are some levels that may not load at all.
Add buffers in chipram to make disk access faster. You can launch the system tool "NoFastMem", then call addbuffers command pointing to the volume where you have the game. e.g.:
addbuffers WORK: 300
then launch the tool "FastMemFirst" to reenable fastram and you can launch the game and it will load slightly faster.
Anyway if the game runs at 2fps with a slightly reduced screen it run slow, I have run ADoom on a blizzard1220 and it wasn´t so slow with low detail and a slightly reduced screen size. Do you have your cpu caches enabled? you can enable them with the cpu command. Maybe you have chosen a slow chunky2planar module?
