Cars serve as more than basic transportation for people. This is a reason why there are so many manufacturers and multiple models produced by a given manufacturer. Toyota makes cars that range in size from that of a Smart Car (the iQ) to a full size SUV that can accomodate 7 people in the Sequoia. The engine sizes range from small in displacement and output to incredibly powerful and built to achieve high speeds, cornering manuevers and other driving feats. For many people the commute to and from work is part of their daily process.
Speed is defined as relative rapidity in moving or going. My question is does speed really matter when you are battling gridlock on a highway such as I-25? You can have a V-8 engine with 550 horsepower but need to merge in with the other guy who's piloting a 4 cylinder Subaru with 170 horsepower. In this case the performance numbers don't matter as the power of a vehicle makes minimal difference in how quickly one driver reacts to the other. There may be the "I'm not letting you in" mentality (I admit to having done that before) but eventually lanes end and the person in the merge lane will have to get over one way or another.
Speed does matter if you're drag racing at Bandimere in Morrison, CO or a professional race car driver; however, that's not what I'm talking about.
In my opinion people follow the speed limit at their discretion. If you're in a hurry to get somewhere you may go 5-10+miles per hour (mph) above the limit. However, it is common to hit the brakes if you see a police car/motorcycle or one of those lovely photo radar vans.
So, does speed really matter?
