They are the same thing. The only difference is the color, Performers are red, classics are gray.
I've got no personal experience with Ebrock shocks, but I've heard good feedback on them for street applications. Track use may be another story as they tend to fade with sustained aggressive driving.
Yes, mono-tube shocks may tend to feel a bit more firm than a comparable twin tube. This is because a mono-tube has more oil to move and as a result may have a higher resistance to motion. This also means that they have bigger discs internally are more sensitive to changes in velocity in their travel and can exert greater control over wheel motion. By contrast a twin tube is displacing less fluid and may feel smoother in its motion. Because it is a tube within a tube, they can still be function if the bod is damaged, where a mono tube will be junk.