It doesn't matter so much what you throw, but whether you miss bats with it. Brad Penny throws harder than Lincecum, but is his fastball more effective?

Bumgarner had 164K in 141IP in 2008 vs. 92K in 131IP in 2009. His K/BB went from 7.8 (LOL) to 2.7

That's why he dropped as a prospect IMO. The decreased velocity probably had a lot to do with it, but it's tough to be certain.