Speed matters more depending on several factors such as :projectile size, intended targets, and distance to target. Those small differences add up in actual combat, were often, both you and the target are moving around. That barely noticeable change can mean the difference between missing and hitting something like a seraph. It would also seem that speed tunes matter more on slower weapons than faster ones. At higher base speed, rates of change is less significant as perceptually, it's still quite fast, however over long distances that speed proves it's worth.
