IF it only boils over when your driving it hard, its not a fan issue. The easiest way to test the fan is to use a multimeter and test for voltage at the fan connector.

You need to have a block test done. While common signs of a blown head gasket are to see mixing of oil and coolant and also to see oil around the head, the most common area to leak first is coolant into the combustion chamber. A block test allows you to test for exhaust gasses within your cooling system to see if the head gasket is indeed leaking.