I'm running the Mahle 18:1 marine pistons, and am decked .010" but running stock thickness gaskets (which should put it around 19:1-ish)
The coldest I have ever had to start it was when it was 12F when traveling out of town and staying at a motel in Eastern Oregon. It was unplugged all night, -and I was still running a so-so set of glows. It took me three attempts to get it chuggin' (I did give it a whiff of WD-40), -once lit, it started hitting on all 8 in about a minute, and settled into a nice crackly-idle in about 1-1/2 minutes.
With the 60G glows installed, I haven't had any problems at all when it's around 35F and not plugged in.
All in all, I love this 18:1 engine and have had no regrets, I'd do it again in a heartbeat.
For whatever it's worth, -I'm old-school with a DB-2 pump.