I get to 3.75, plug in the sd card with the rcmloader, and there is where I get the stupid GPT error. again.
*edit*
Oh my god, I found it. It's stupid as all hell, but god I found it.
in the emummc folder, there was an ini file, likely with configuration settings. ONe of the entries was about the sector. The sector listed was valid for the old, 256GB card. But it's different on the new card. Copying the sector entry from emutool into the line for the emummc ini file? It boots now!
Now can I restore my emuNand?