With a half hour or so spare this evening, Ive collected up some tools and bits for a little 'out-of-workshop' project building, namely the 2nd Chinese Pixie-2 kit I had kicking about, but also had chance to add the modification resistors to the keyer
This is the 18k series resistor (making 19k with the 1k that is already on the board), and the 39k parallel resistor across the 100k potentiometer.
Well, I havent measured the speed range maximum and minimum yet, but by ear the minimum sounds like 5wpm, the maximum like 40 or 50wpm. And right in the middle of the range are the speeds I want!
I will rig the keyer up to some software later that can tell me the actual speeds, so I can make up a scale for the control. But it seems the mod has done the job.