RP, welcome. Design techniques such as using a driver with a very long excursion capability and applying high amplifier power to it can to a certain extent compensate for size in a sub, but in general a good big one will beat a good little one. Users are generally satisfied with the Sunfires, but if you can possibly fit in the EP500, you'll get significantly more capability.
On the size of your room, keep in mind that there's no requirement for it to be "filled" to the farthest reaches at adequate loudness levels; this is usually only needed at your regular listening position, which probably would be about 10-12' away. The M60s should serve excellently when powered by any of the receivers with ratings in the 100 watt area.
