I would say that it is situational. A commute I had years ago had a section that was congested and the cars were only doing about 20-25. I found out that I felt a lot more safe by pushing hard during that section, taking the lane and going with the speed of traffic. If you are going a lot faster than surrounding traffic, then you are setting up some potential saftey situations, and of course things like rocks, potholes, mechanical breakdowns are amplified by speed.