The six relievers who got the most playing time for the David Aardsma, Sean White, Shawn Kelley, Miguel Batista, Chris Jakubauskas, and Mark Lowe. Here's how they did pitching to Rob Johnson and Kenji Johjima (Jak's starter stats are included because I didn't feel like separating them, but he conveniently threw to each catcher about equally often as a starter).this year were
You'll see that, over remarkably similar sample sizes, the relievers walked fewer batters when throwing to Johnson than when throwing to Johjima. The other two stats aren't meaningfully different.
But wait! That's not a fair comparison, because the playing time distributions aren't the same for each catcher. For example, Johnson got to catch 50% more Aardsma, while Johjima had to catch 60% more Batista. What happens when you weight Johjima's numbers to equal Johnson's PT distribution?
Johnson: 7.5%, 17.3%, 2.5%
Johjima: 9.3%, 16.8%, 2.4%
There you go. Neither the strikeout nor home run rates are meaningfully different, and the walk rates are within two standard deviations of each other, but something to think about.