First of all, have you isolated the problem to the BVision by running WorkBench in AGA mode and see how it behaves?
In "normal" screen modes (i use a hacked version of super27, enabling 800X600V256collors) Workbench behaves perfect...
No problems at all. Multitasking, playing games, watching pictures and videos (though I have not found a good player yet, and only get like 2FPS). And i cannot complain at all for AGA modes. But when changing screen mode to the BVision card The whole system freezes up. sometimes it can work for some minutes, once it worked for hours. But it always freezes, eventually... I have tried to change to another aga mode to check if there would be problems between super72 and the CGX mode... but nope... no matter what i use, it freezes up...