one ohm load might make your amp run a little hotter, and the thd goes up the lower the ohm but thats about it, i don't think your amp would fail as long as its 1ohm stable.
if a amp is stable at 1ohm then it is fine to run it at 1 ohm. Is it better for the amp to run at 4? yes it will run much more efficient, and cool. With that though you most likely lose a good amount of power 1/4 amount the power from 4 ohms to 1 ohm typically. Unless your amp is a regulated power supply then the power output is the same accross the impedence table. At 4ohms you draw less current from your cars electrical system and your amp runs better in a nutshell(unregulated power supply)