Greetings, and welcome.
Well, I'll take a swing at it...
There are many board regulars that have owned both models that are qualified to describe the differences in sound. I am not one of them. I have heard only the M60, and am very satisfied.
You may wish to consider not only specifications, but also lifestyle. To get good sound from bookshelf speakers, they must be placed on stands. Personally, I disliked not only the expense and aesthetic of stands, but also their potential to be knocked over by my idiot dog or only-slightly-less-dangerous children. The cost of speaker stands closes the price gap somewhat between the two.
Some people believe that smaller speakers allow better imaging. They certainly are easier to move and somewhat easier to place. Some people believe that floorstanders present a bigger, fuller, richer soundstage. I generally agree with that camp.
While 80Hz is a generally accepted crossover point, you may find (like I did) that - for your ears in your room - 60Hz makes the bass more difficult to localize and provides a somewhat smoother response with the M60's. There are few absolutes, especially since the room is such an important factor. How big is your room, anyway? And what proportion of your use is devoted to music vs. movies?
Those are important considerations. If you are primarily interested in movies, you absolutely need a sub sooner rather than later. Even though the M60's provide excellent bass response, you really need a sub to produce meaningful LFE for movies. With music, in most cases, the differences are much more subtle.
I bought my M60's and used them without a dedicated sub until I could afford a good one. Doing so allowed me to enjoy music fully right away without fear of future upgradeitis, but adding a sub was a very dramatic improvement for movies.
