Does Extra Rest Really Help Pirates Pitchers?

The Pirates have gone to a six man rotation. There's no way to know how long it will last, but for right now they are rotating six starting pitchers. That raised an interest in my mind to say how well our pitchers have done in their careers with an extra day of rest. Here's some data:

Pitcher	Rest Days	ERA	BAA	K/9	K/BB
A.J. Burnett	4	3.96	.246	8.4	2.4
A.J. Burnett	5	4.12	.239	7.7	1.9
Wandy Rodriguez	4	4.10	.261	7.3	2.4
Wandy Rodriguez	5	3.58	.241	7.5	2.5
James McDonald	4	4.68	.250	7.8	1.7
James McDonald	5	3.97	.258	7.6	2.4
Jeff Karstens	4	4.05	.279	5.2	3.0
Jeff Karstens	5	4.07	.264	4.3	1.7
Kevin Correia	4	4.73	.271	5.7	1.7
Kevin Correia	5	4.42	.278	5.7	2.0

The data is pretty random here. Burnett, Rodriguez, and Correia are the only ones with big enough samples for this to really mean something. It seems that Burnett pitches a bit better with a five days of rest, but it's the other way around with Wandy; he pitches better on four days of rest. McDonald and Correia seem to like the extra day off as well, and Karstens pitches the same regardless, which doesn't surprise me one bit - numbers just don't ever show anything with that guy.

To me it would seem like it really doesn't make a very big difference whether guys pitch on four or five days rest. I'm not sure the goal of this is to improve their every game performance either, but more to make sure they can make through the entire season still pitching close to the top of their physical ability.

The numbers don't really tell us much of anything here, but it was interesting to see at least, right?