I need a new bike for commuting. I wrecked my last bike by rear-ending a silver Lexus. The fork collapsed into the frame. Yes: I was going that fast. The frame was a light street-frame, already showing signs of wear from the load. I'm pretty serious about cycling: I think the world would be a better place if we could get all those cars off the road. I really like to go really fast, 'cuz I'm always in a hurry. I really hate pulling out my bike and discovering a problem with it, for the same reason: I'm always in a hurry.
I ride on surface streets in Los Angeles, often in traffic, usually dry weather. I weigh ~225# and I carry cargo: groceries, change of clothes, etc.
So I need a fast bike that's sturdy enough for those conditions. What kind of gear should I be looking at? The frame is really the only part that *has* to be replaced, but I'm not even sure what class of frame I want. Are mountain bikes sturdier? Are they just as fast?