My BVision worked fine with the CGX that came with OS3.5 (ther was a version of CGX3 shipped on a floppy with the card but I only needed the driver component there). I've never had any problems getting it to work (bar the fact my first one had a faulty memory block annoyingly situated in the 4-6 MB range).
However, I did buy CGX 4, simply because I wanted to keep up to date and make sure any RTG coding I did worked on CGX3 and 4. Under OS3.x I've never had any trouble with CGX.