I wouldn't be obsssing about the effect of wind chill vs the temp of the block, the important thing is the temp of the water IN the block. The moral of the story is, you pull your boat out, or stop using it, and just winterize or at least drain it right THEN! Don't wait or you can get caught short, and have to run out and freeze your thumbs off draining the motor. I usually pull mine out in mid Oct, and that next weekend it gets winterized. Engine oil change, oil filter change, drive oil change, fuel filter change, engine fogged, engine/manifolds drained, BACK FILLED with -100 AF with corrosion inhibitor. Sprayed down with Boeshield and that's all folks, no big debate about wind chill or how long it takes to crack a block.
I have a neighbor who leaves his boat in till mid Dec (salt water), it just sits there not used, since Sept, I don't get the point, then every year when he finally winterizes it he's complaining that he had ice in the impellers (but the engine is closed cooled so it's ok). Why do it it the hard way, the easy way is so much nicer...