I have tried both CV PPC and Voodoo3+Mediator. (I own both).
Mediator is faster, CV PPC is a bit slower but on OS3 it has the advantage of promoting 31KHz screens, at least for A4000 users. Some may argur CyberGraphX is better, some may not.
Voodoo 3 on OS4 is by far and away a hands-down winner. The 16MB graphics ram really, really, really makes a huge difference, and it can show the early startup too, once the OS4 kernel is loaded. It's faster, too, on OS4. Works great with Mediator.
