Well, as it turns out, I didnt have anything really repeatable after all. Most of the time I boot without a code error, sometimes still get the code 43, sometimes code 12. All three ways I cant seem to actually use the igpu for transcodes on plex. At this point, I've essentially spent a couple of 40 hour work weeks trying to debug this with every possible combination. I've even tried, as someone said somewhere on this forum, saying Spaceinvader One in the mirror three times, and still have yet to see it transcode again... I'm done.
If anyone else has the Intel Hd 4600 igpu passed through to thier windows VM I'd love to:
1. See your XML
2. Know whether you're using UEFI or Legacy Boot
3. Know whether you have another video card on board, and which if any HDMI ports have a monitor attached
4. Know what version windows drivers for the 4600
5. Know if you modified the Unraid Kernel
Without a little guidance from someone who has this Igpu functionally passed through, I surrender.