Remember the difference between freeze protection vs burst protection. Everyone here is using freeze protection numbers, but to protect the block from cracking what you want to pay attention to is burst protection.
Freeze protection: The temperature at which crystals start to form. This results in a slushy mix, one that does not completely block flow or expand in volume.
Burst protection: The temperature when the crystals & slush solidify into a solid mass, and volume increases to where in a restricted vessel the pressure would cause bursting/cracking.
Here's a table for Ethlyene glycol, the stuff we usually use:
Note that a 52% solution (52% glycol and 48% water) will give freeze protection to -40F, but only a 37% solution is required to provide burst protection to -40F. At 50% glycol, you are protected from burst to over -100F, not a temperature any of us will ever see.
Also keep in mind the higher the proportion of glycol, the more your cooling efficiency goes down. Glycol is less heat dense, it carries less heat away from the engine. If your car doesn't overheat in the summer with 50/50, then you won't care, but if your engine gets hot, consider reducing the glycol percentage you are running to 1/3 glycol to 2/3 water, that will give you burst protection to -25F. Your climate obviously affects your decision.