It may be less a question of which speaker will be better to fill your room, but more of which type of sound you prefer. General consesus is the M50s are a tad more laid back in the midrange vs. the M60s. There is good info to be found if you run a search of the forums. Either way, you can't go wrong.

What type of speakers are you using now?

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"Nothin' up my sleeve. . ." --Bullwinkle J. Moose