E-M energy, whatever its wavelength, doesn't always travel at c. Remember your winter coat? The 'bending' of the straw in a glass of water?
Got a cite for that? The "winter coat" and "bending straw" analogies are irrelevant. Niether prove your contention that E-M radiation will travel at less than the speed of light. Speed of light is a constant, at least according to Einstein. Your examples can both be explained without the need to change a constant.