Actually,
Antifreeze won't raise the boiling point of your cooling system. It's main purpose is "Anti-freeze" as well as having rust inhibitors. All cars have a 50/50 ratio in them as they leave the assembly line for no other reason than nobody can determine who will buy the car and what climate they live in.
The "boilover" point is determined with the following formula:
(this will vary at altitude)
H2O boils at 212 degrees.
Each pound of pressure of your radiator cap is good for
approximately 2 degrees in rise of temperature.
Thus a 19 lb. radiator cap X 2 degrees per pound =38 degrees of additional "boilover" protection.
212+38=250 degrees.
But as I stated earlier, you do need to use "Deionized water because of it's total lack of mineral salts and metals. A rust inhibitor is highly recommended.