On AGA, a turbocard with MMU greatly helps speeding up the graphic refresh, I remember that on my 1200 with a Blizzard 1230 a 256 colors screen was fast enough for most games, using the Savage driver.
Since your CPU lacks an MMU, I suggest you try all the alternative AGA video drivers which don't require an MMU, like AGABoost or AmigaAGA-EVD, you might be able to get an usable 16 colors screen:
http://aminet.net/search?query=shapeshifterVarthall
