You need to take a huge dose of salt with those bandwidth figures. They are theoretical figures for top speed at which a pair devices sharing the bus can communicate.
From experience I can say that the bandwidth from the CPU to devices on the bus is much slower (about 15Mb/s is tops on a 68060 A4000 with mediator).
As a result of the slow bus speed, faster processors can't keep the cards fed with rendering instructions fast enough to make full use of their capabilities, even on the Voodoo3 and above.
