When your amp is clipping, your music will generally sound compressed and quite distorted. As far as over-excursion, I've overdone that to the point (long ago) that the speaker cone bottomed out and made a loud 'thwack!'.
I experienced the former with too little power and the latter with too much power (or rather, poor judgment using a lot).
I experienced the former with too little power and the latter with too much power (or rather, poor judgment using a lot).