M60s all the way. They're easy to drive and in a room that size will fill it beautifully. M80s, while fantabulous, are not absolutely necessary for a room that size, and are much harder to drive.

Just my $0.02... YMMV.

---- A Woofer in Tweeter's Clothing... M60s, VP150, QS8s, EP350 Onkyo TX-SR702, Denon DVD-3910