Alas, ggw, because the numbers are NOT favorable to Bush, I'm tempted to believe the Cato numbers -- and I believe they hated publishing them.
Similarly, if the Progressive Foundation reported that Kerry voted against 200 important tax cuts for the middle class, I'd believe that as their finding is not supportive of the organization's overall mission. But, if you have to decide, I'd err on looking for other sources as I believe Cato has a transparent bias.