I'm in the minority here, I use the cheap $35 Campmor rain cape. Aerodynamically they suck, so riding as fast as you describe is out of the question, it's like pushing a kite in front of you. That being said, they work for keeping you dry and allow a lot of ventilation to reduce the heat and sweat. When I have used rain suits it was like a toss up, get wet from rain or sweat. Given the choice, it depends on the temps, above 50 F I'll take rain, below I'll stay warm and take the sweat. I like mine, it keeps me on the bike when it rains, and it is usually more comfortable than getting wet.

Marc