it has been my experience that black does like a little hotter temps than white does.

as for "overheating" your hotend - there should be a temp value set in the firmware to shut it down before it gets hot enough to damage the PEEK. On my SD4 that was at about 225C.

for a potential replacement, I can highly recommend the E3D v6, or the Lite6 if you are on a budget.

Hmmm...wonder what those values are supposed to be.  I'm running modified firmware for bed PID so it's possible that it doesn't have that safety feature.

as for "overheating" your hotend - there should be a temp value set in the firmware to shut it down before it gets hot enough to damage the PEEK. On my SD4 that was at about 225C.

for a potential replacement, I can highly recommend the E3D v6, or the Lite6 if you are on a budget.

I guess if you know that black used to print fine on the hotend at 205C previously, it's more likely that something else is amiss.

WRT replacement parts, if you do suffer a failure, there are a range of reasonably priced hotends out there that would serve as an excellent upgrade from the stock hotend. With a printed extruder (lawsy) you could use an E3D v6 lite, for example.

I'd try cranking the temp up 5 or 10C and see if that helps - you've got a bit more room to play with still.
Even without bubbles, moisture could still be partly to blame here.
Smooth flow sounds like clog is unlikely, but they're not always consistent or obvious!

I don't think I can...won't that damage the printer?

I've always been under the impression that the PEEK insulator will start to melt/deform around 210C...I'm already quite close to that or I would go higher.  And now with Solidoodle going downhill, I regret not buying any replacement hotend parts.

Sounds like you might have a partial clog.  If it used to have enough torque but no longer does, that seems to indicate that the force to push it thru the nozzle has increased.

I'm not sure...I know black has always been harder to extrude and if I change to white it runs like a dream again.  Wouldn't a clog affect all colors equally?

The extruded filament doesn't curl or sputter, it's a smooth straight flow just difficult with this Octave brand black (white is also Octave brand).  Both filaments are about a year and a half old, though it isn't bubbling as if it's humid - as I say when it is working it's a smooth flow.

What is the correct resistance values for the stepper on the extruder?
I'm reading about 31-32 ohms resistance on the wires to the stepper when I disconnect it from the controller board.

I'm printing at 0.1mm, basically the default Solidoodle settings but with honeycomb infill.  Bed temperature is 97C and hot-end temperature 205C.  It's year-old black Octive ABS filament.  Normally I run 0.2mm with white, but it runs on those settings like a dream, even at 250% speed.  This is clicking at 100% speed even, and I can see the "gear" move a bit forward and back.

I know it still has enough torque to tear out the filament, because that's happened a couple times too, so maybe it's not an issue with the motor, but I would still like to know the proper values.