spcomputing:
@strykeroz - I found the "burn bootloader" isn't necessary with core13 for setting the clockspeed because the high and low fuses come from the boards.txt. I just select the 128kHz board and upload the sketch (Don't even have to select Upload via Programmer).
nice one. I defer to your experience on that as I have settled on ATTiny85 as pretty much my weapon of choice 