Given the same amount of power in the M80s will play louder than the M60s. The amount of power required can vary widely based on two main factors: 1) The size and characteristics of your room and 2) Your idea of loud. To achieve above average output in a large room cleanly takes a lot of power because the actual output is not a linear equation to the wattage. So that last bit of volume will take a lot more power to achieve cleanly. This being said, it will be easier to achieve with the M80s than the M60s due to their output per watt being higher and easier with the M60s than the M50s and so on as you move to smaller models.
President & Chief Engineer