It's wierd, I thought a percent or two change in speed wouldn't make much of a difference, but it does. With the speed-up you get an increase in frequency and also a change in timing. Not only are voices pitched higher, but the music has lots of extra snap to it. If you have a recording that seems dull and lifeless, just speed it up a bit, and man, it'll gain a new life.
Since we like to compare and grade our cables, power cords, and what not, I'll go out on a limb and say the tonal changes from the speed-up is a lot bigger than a cable change. At first I didn't notice the difference so much, but now that I'm keyed onto it, and I notice it immediately.