I'd be careful about trying to lose too much weight too fast here. A lot of fad diets promise miracle results in this aspect, but these often lead to other health problems much worse than being slightly overweight. I also don't believe there is an optimum % in this area because everyone is different. Some people will have a higher % naturally than others will.

Basically, I think yuo should be a little careful in trying to set absolute goals in this area.