The Yellow King is specifically made for use with carbon fiber rims. They provide unparalleled stopping power in both wet and dry conditions. They give you high durability, quiet braking, and perhaps best of all, excellent stopping power with aluminum rims as well.
The FlashPro has deeper asymmetrical grooves and a more pronounced leading edge profile, with the aim of moving more water to improve wet weather performance and the deeper grooves also help give the pads better modulation. They increased the total pad depth with more material above the wear line.