Now that's another idea. The Creamback H at 75W would certainly provide the extra watts needed. I see it has 100db sensitivity, so fairly loud. I quite like the tone on this clip (a bit brighter than the M65, but that's a good thing):
https://www.youtube.com/watch?v=du5sn1wtZWA
Actually, the amp provides the watts, the speaker's rating isn't going to increase the amp's wattage, it only states how much wattage the speakers can handle before they blow up. However, a more efficient speaker will be louder with the same amp, as long as the amp puts out the power the speaker is rated at.
Sensitivity of a speaker is usually measured in how many db the speaker produces with one watt of power. It'll be a little louder than the 65 at one watt with a 1Khz tone in an anechoic chamber in a lab.
But the speaker's efficiency in the real world also depends on the cab it's installed in (a sealed closed back cab makes a speaker less efficient due to the air pressure inside the cab, an open back cab is a more efficient setup but dissipates the sound and reflections from the back of the cab can cancel out various frequencies depending on speaker placement in the room, etc), and of course every speaker presents a different load to the amp at various frequencies. So these specs have to be interpreted with that in mind. Different amps react differently to a speaker load, too, due to things like the amp's damping factor.
So a speaker that's more efficient and louder at 1 watt with a 1Khz tone can be quieter at, say 500 Hz, and much louder at 2000 Hz, as an example. This is why some speakers sound more scooped, or more spiky, or have more or less bass, when connected to the same amp.
Remember, too, that guitar speakers distort a great deal. If you have a 50 watt amp, there's no measurement on a spec sheet of how much volume the speaker delivers before it starts to break up with more than one watt. Speaker breakup will tend to affect the ultimate volume of the cab, and they all break up at different power levels.
In other words, speaker spec sheets can fool ya. Being part of a system (i.e., amplifier, cabinet, speaker), the various parts of the system have a huge effect on one another.