40d?

At the moment i am working with a 30D for my bird photographs. When shooting birds in flight i do not have a lot off keepers. Maybe it is the technique, but i really think that it is the AF of the camera. Sometimes i have the feeling that the 20D was better for BIF. Are there seasoned 40D shooters around with real experience of the 40D over the 30D who like to share their thoughts on this issue?

By the way i am photographing with 500/4 + 1.4tc

Thanks for your thoughts and insights on forehand!

A 40D might be a little better (I don't have one) but depending on your budget, for BIF you might get a (used) 1D Mark IIn. Just look at Jody Melanson's images, that should say it all. :)

I have used the 30D, 40D, 5D and Mark 2 for BIF. If you really want to get serious with BIF, get a used Mark2N, it is better than the others I have listed.
I find both IQ and AF to be better on the 40D than the 30D, at least with the two I have. Noise is a little better on the 30D than 40D, once you start shooting high ISO's(say above 800), but realistically, it's something that is easy to control. I do find that the 40D AF points to be a little "hard-edged", aka. if you drop off the target it will go looking.