OK, the 8500 came in four different speeds...
120, 132, 150, and 180. Each of those machines had the following bus speeds
40 , 44 , 50 , and 45 MHz.
That much I know, but the rest is confusing. Based on that, I was looking for an 8500/150 to use as a server. I was planning on eventually upgrading the processor to a slow G4. So I wanted an 8500/150 to start with because it has the fastest bus. But I just read that the but speed is controlled by they processor card. Does this mean if I drop a 150MHz processor card in an 8500/120, the bus will run at 50MHz? And does this mean that the bus will run at 50 MHz in any 8500 that I put an upgrade card in? It will make a big difference as 8500/120's go for much cheaper on ebay! :-D