Hello FosterCO,
That is an enormous room. I would not feel comfortable driving M60s in a room of that volume with less than 100 watts per channel. Given the penchant of many enthusiasts to "crank it" with great-sounding speakers, especially at parties, I think you should seriously consider upgrading the amplification. Forget the audio jewelry and divert the funds to more amplification capability.
By the time you "listen for clipping" in a room that size at high volume with 40 watts per channel, you may well have already damaged one or more drivers.
Regards,
Alan
