The VLB machines I use are 486 class (there are some rare 386/486 hybrids with VLB but they suck), the caching controller has a Harris 286-20 chip on it to offload the real cpu of the task of moving data around.

I have a RavenPro PDS (040 PDS slot) here somewhere, they should be the fastest 68K Mac SCSI card made. One SEIV will saturate the Nubus bus with a couple good drives, with PDS you can get a bit more speed.