the coldest start I ever had was about ~15 F, it cycled for about 30 seconds before the wait-light went out, then it fired right up (I kept the pedal floored while the starter was turning, when it ran by itself I released it) and I had some smoke for a minute. If its that cold it can idle a few minutes before I start to drive (Also I dont really push it until I get warm air out the heater-blower..)
I have a new GP-controller and a new GP relay installed, all stock except the doghead mod. I never had to try a few times until it ran (despite the times with the dead batterie, burnt controllercard and bad gp relay..it didnt start then)
I still run the old glowplugs...when one of those will fail I´m replacing them all, have a set of 60g´s ready to put in.