Many GMs say that G/B ratio and velocity are meaningless for pitchers. While I agree that control is far and away the most important rating for pitchers, I disagree with most on G/B, velocity, to a certain degree P1-P5.
Orlando Romero is a good example of how important pitches are. Control and splits are pretty mediocre, but he has 5 pitches rated 52-89 and he has a career ERA under 4.00 with a .255 OAV. Not an ace by any means, but good, solid starting pitcher.
Ricardo Cornejo is an example of how important velocity and G/B are. Splits are only in the 50's (also has very good control). Career ERA of 3.88 and 1 All-Star appearance as a lock down closer. I picked him up off the scrap heap for $1.5mil after FA period ended.
For me, I pay special attention to Control, velocity, and G/B for my closers because 3 things I don't want in a close game in the 9th inning are walks, balls in play, and home runs.
Nigel Alexander is my current closer. If you couple velocity and P1 both over 90 for a relief pitcher you've got a strikeout machine. Think 2004 Brad Lidge.