So, more info on the burning smell. I had a friend in the car at the time so it was good to get a second opinion. He was sure it was coolant that he was smelling. Even before it was really bad he could smell it faintly. To be honest my nose for certain types of automotive fluids either burning or not is pretty newbish, so my initial description of the 'electrical burning' is likely incorrect.
Here's what I did to 'break it' this time. From a slow roll pinned it to 7k RPM in first gear. Slowed, then smoke started entering the cabin on the passenger side primarily. Stopped the car with the engine on and rolled down the windows.
My friend thought it might be the heater core that was leaking. He's not a BMW guy but it's a possibility just a PITA to get at and fix. I'm not familiar with heater core failures so I need to read up on that.
My other other thought was the valley pan gasket having a minor leak that is under high RPM load and pressure opens up and squirts coolant out somewhere. Is that possible? It was definitely the higher RPMs that cause this situation to arrive. Under normal driving conditions this doesn't happen, although there is a faint odor here and there.