Here's some info on how different strings sound. I found this at guitar.about.com.
StringitUp!
The bottom line is that 80/20 refers to acoustic strings that are composed basically of 80% copper and 20% tin. Sometimes called a Bronze alloy. Then you have Phosphor Bronze, which are a little smoother sounding, which are 92/8 composition. Phosphor is added to the alloy.
Steve