Sounds great! I agree, unless there is foam on the underside of the oil cap or on the dipstick, I wouldn't bother with the oil. This really all does point to the radiator cap being worn/weak and just not holding the pressure needed to raise the boiling point. Most coolant boil/freeze charts assume the cooling system is pressurized to 15psi.
Note the column at 0 psi with a 33-44% mix; pretty much right where you boiled over. Fun fact, the C7 uses a 20psi cap (most are in the 12-16 range) which explains why it can run such hot temps without boil over issues.
Hybrid Mode
