I was surprised by how well it ran actually! Remember this is only a 68040 running (well, walking!) a 3D game under emulation.
Personally I use my beefed-up 50MHz 486SLC/2 A2386SX bridgeboard with 13.5MHz ISA bus. Only problem is no sound card I've found so far can cope with the overclocking of the ISA bus, but it made an appreciable difference in speed of Doom.
Ultima 7 runs nicely though, and Alone in the Dark is also good.
My next test is to replace the 386SX bridgeboard in one of my A1500s with a 33MHz 486SLC and see if the upped bus speed from 25MHz to 33MHz makes much difference. Means swapping the northbridge as well as the CPU, but because the bottleneck on the 386SX platform is the 16-bit memory bus, I think that extra 8MHz may make a difference.