Unfortunately I'll be rather busy until mid April this year - here is my plan for the time being:
I'll reinstall Linux Mint Cinnamon, integrate memtest86+ into coreboot and run it. I'll report back if it's just bad RAM or something else.
Since my T430 was modified a couple times I'd also suggest we try to find someone with a more stock T430 to see if your HT patch works. The X230 somewhere in this thread worked and I'd argue that it does work properly on unmodified Thinkpads.
Sorry for a long reply too. About mrc.bin: no, it's actually possible to use mrc blob on Sandy/Ivy, but as I see it's not supported across all boards. X220 has support, other boards needs patching (or maybe patches are already on gerrit, I'm not sure). It shouldn't be hard to get it working, though.
Can you elaborate on this one? Why does the X220 has support and other Sandy/IvyBridge based laptops are not supported? Wasn't one of the ideas for coreboot to have a more common code base or am I missing something obvious?