@Nightshade737
Actually, the Mediator doesn't plug directly into the daughterboard slot. It consists of two different pieces:
1. New daughterboard with inactive PCI slots, replaces the original one.
2. Zorro -> PCI bridge that interfaces the inactive PCI slots on the new daughterboard to the Zorro bus.
So the mediator interfaces it's PCI bus through the Zorro-bus, just like the Prometheus. No speed gain there, just a much neater and prettier solution.
The G-Rex, on the other hand, should be fastest solution, as it is connected to the "PCI"(?) slot on the Cyberstorm MK3 boards. But I believe the G-Rex is no longer being produced.
-Edit-
Oh, and if the Mediator eventually interfaced directly on the daughterboard, it wouldn't make any difference, as the daughterboard-connector is just "plain Zorro". The daughterboard is nothing but a riser-card.