Rain cape. I overheated in a =snow storm= with a "breatheable" rainsuit, and still got wet. The rain cape was too chilly by itself, even in a warm April rain... I found myself wishing for a light jacket. You may want to team it with some "rain legs" depending on your size and bike. I have a pedal-forward bike and I'm roughly the same size as an over/under washer/dryer set, so my knees get wet in torrential downpours (but not my lower legs, weird)... a more traditional riding position and a less substantial figure and it's just about a perfect solution.

It does catch headwinds like nobody's business, tho.