But under windows it supports full gigabit? And has been for 4 years.
After diving into this for a couple hours it seems that kernel is misidentifying the ISA Bridge ID.
What it's looking for is the SiS965 and what I have is the SiS966
00:02.0 ISA bridge [0601]: Silicon Integrated Systems [SiS] SiS966 [MuTIOL Media IO] [1039:0966] (rev 59)
As for the Ethernet Adapter is presents itself as.
00:04.0 Ethernet controller [0200]: Silicon Integrated Systems [SiS] 191 Gigabit Ethernet Adapter [1039:0191] (rev 01)
It seems like I need to change/add the Bridge ID for the SIS966 in the kernel to match what I have. This is above my pay grade.
Also, Statically setting the negotiating speed on the switch (all three - Cisco, Mikrotik or the Netgear) to 100mbit Full Duplex has no effect.