What do you suggest?
You want to the regulator to run 50 / 100ma at least. So I would use a resistor of 8 - 10ohm, give or take. Higher where the voltage dropout is big.
so the regulator can be very hot at 700mA?
Yes, particuarly if the Vin-Vout is large. Your heatsink is puny for this type of applications.