Hmm. Well, I opted for the 80s over the 60s for an apartment livingroom that is 20x11x8 and I wasn't even considering them before I did an a/b comparison.
No doubt they will go much louder than I will ever need, but they also present more detail in the mids and highs, and more bass extension.
I really noticed the extra detail with cymbals and the kick-drum, and to a lesser degree with other instruments.
I think that it depends on what music you are going to listen to and how well recorded it is. In my case, I was auditioning with Dire Straits, Peter Gabriel and ELP, all well recorded albums.
I will be listening to a mix of (well recorded) rock, jazz and classical so I will benefit from the step up to the M80.
If you look at a post by sovkiller you will see that not so great recordings sound not so great on the M80 because of the detail they present.
Hope this helps.
