The Inferno is essentially unobtanium, I can't even find a decent picture of one. :-( According to rumors it does exist, and there are CGX drivers for it. The only practical advantages I can think of over the Phase5/GVP cards are DMA ethernet (no MNI driver AFAIK) and an overall slight performance boost at the same clock.
In regard to the Z2 bus - yes, this can be a bummer when the Z2 bandwidth is exceeded, but this isn't always the case. 1024x768x16 is plenty fast here, even with AfA eycandy on. (GFX benchmarks like P96Speed won't show a difference beween Z2 and Z3 at lower resolutions, either.) RTG scenedemos are nice and smooth, PIP stuff is fast (and resizing said window is fast), webpages that work well with IBrowse load quickly, scrolling through them is also fairly snappy (much faster than AGA). Ethernet is no problem with a fast CPU, the Z2 bus is still enough to handle most internet connections with room to spare.
Not to say Z3 isn't superior, quite obviously it is, and in some circumstances Z2 will limit performance. (If you're going to pick one machine to expand, the A3000/A4000 is a better choice.) However, for most basic use I've noticed little difference. As far as classic hardware goes, DMA ethernet (Wildfire is fastest ethernet on classic miggy), SCSI, and a good gfx card would still perform well overall, even with Z2.
