I have been listening with interest over the past few days to the ABC radio discuss whether Brett Lee or Mitchell Johnson is the faster bowler. Largely, they are using the figures generated from the speed gun as a guide. Whilst velocity readings are very interesting, I don't think they come close to telling the whole story about how fast a bowler is. I admit that what I am going to say will probably confuse everyone but here goes; I don't think that the velocity of the ball is the same as the speed of the bowler.
What I mean by this is that some bowlers are perceived by the batsman to be faster than others, even though the measured velocity may be the same. A few years ago Glen McGrath was measured as being slower than Greg Blewett. However, if you asked opening batsman which one was faster, I assume all of them would pick McGrath.
My feeling is that batsman tend to find certain bowlers 'faster' than others on the basis of having to make a late adjustment when the ball is not quite where they expect it to be. When the ball is delivered, the batsman immediately starts moving into position to play the shot. With only half a second or so from the bowler letting it go until the batsman plays the ball, the batsman has to move on instinct into the correct position.
Brett Lee at 135kms/hr is far 'slower' than Clark at the same velocity, as Lee has a very flat and predictable trajectory. This means that the batsman is in position to play the shot earlier than against Clark, who tends to achieve extra bounce or movement off the seam that forces the batsman to readjust their shot from what they expected. This then makes the batsmen perceive the bowler as being faster than what a pure velocity reading would suggest.
Likewise, if a bowler has an unusual or strange action that prevents the batsman getting an early sighting of the ball, they will appear faster. The great South African Mike Proctor is an example of this, as his "wrong foot" action meant that batsmen were not picking the ball up early. Velocity tests showed that he was not as fast as other bowlers going around during the 70's, however, most batsman rated him as amongst the quickest.
I will concede that 160kms/hr is bloody fast no matter what!