It also depends on whether your system is going to be set up in one corner of the room or using the entire room, and what kind of volume levels you are looking for. The issue is pretty simple -- if you want high sound pressure levels in a large area you need to move lots of air and that means bigger speakers. On the other hand larger speakers cost more if you don't want to compromise sound quality.
If you want high quality sound at "reasonable" volumes then the system you picked should be fine. If you want to "rock the house" with movies or loud music then something larger would probably be a good idea.
If you are setting the system up so that the listening area is only a portion of the room then a bigger sub would be your first priority.
Can you describe the kind of listening you are expecting, and maybe another system you have seen/heard that seemed to deliver the kind of sound "experience" you are looking for ?
I'm asking because there are HUGE differences in listening habits between people, and that affects the kind of system they need. As an example, I was really happy with an M2-based system for movies at moderate volumes (albeit with a big subwoofer), and it was only really music playback that pushed me to M60s.
Having said that, once I *had* the M60s and started cranking the volume on movies I was astonished. It just depends on how much you are going to reach for the volume control and say "Hey, listen to THIS"
