[Jaeson Koszarsky]"Were the Quadcore G5s using PCIe supported by any Media100 hardware?"
They were supported with the Aja line of cards (LHe, LSe, Kona3,…). You should have a look at the Kona drivers to find out which one was the last to support PPC cards.
[Jaeson Koszarsky]"What was the last version of Media100 produced that supported G5s?
Media 100 Suite V1.7.1 From the Release Notes:
Media 100 Suite integrates with AJA® hardware including their Kona3, 3G, LHi, LHe and LSe cards as
well as the entire Matrox MXO2 line of I/O devices and several devices from Blackmagic Design,
including the Intensity Pro, DeckLink SDI, DeckLink Studio and DeckLink HD Extreme.
This release supports Apple Inc® Computers with Intel processors and PowerPC processors running a
minimum of Mac OS X 10.5.8 Leopard or 10.6.2 Snow Leopard.