Well I have a little unintentional experiment running.  

The printer started to smell a little stronger than usual, so I looked at it.  The thermistor code has stopped reporting, so it is now running locked to whatever PWM rate it was feeding the extruder heater at that moment.

As luck would have it, the PWM rate it got stuck at is a little hot, but almost right..  So I've increased the print speed to 125%, and now the temperature is within range.  :)

The print is 3/4 done, so it would be a shame to stop this 17 hour print now.  

We'll see if this works..

EDIT: Temp was creeping up.  More detail in upper layers = less extrusion.  I'm now at 185% to maintain temp, but it's working..

EDIT: Now at 210%...

EDIT: Now at 265%.  Infill is at ~160mm/sec and perimeters are at 80mm/sec.  9% left to print....