>> Radeon X1900 mac version (very hard to find and expensive)

> Apple X1900GT [...] are easy to come by.

Yes, but price very much depends on your location. Currently, eBay Germany only lists an offer by a US dealer (59 EUR + 54 EUR shipping, new, more than 10 available). 113 EUR for the card is pretty steep.

>> Lack of drivers for:
>> - builtin network card (i need to use Realtek on PCIe)
>> - fans (always on middle speed)
>> - temperature support

> I doesn't seem fair that you would restrict use of PCI-E G5s to
> developers based solely on the network support issue.

That's why it isn't based solely on the network support issue, I guess ;-)