This was taken with the 7D and if you read this post I did last week, in particular the second link, I can tell you how relevant this thinking is for this image.
I took some images with the 1Dmk111, 500 + the 1.4 extender, but to get an equivalent crop to this size, I was down to something like 4.1MP. Now that is fine for the blog, as I only tend to post at something like 800 x 600 max. (click image for full size viewing). However, with the 7D file sizes, the equivalent crop was 11.6 MP or thereabouts. So as you can see still more MP's left than I started with on the 1Dmk111. So very printable in terms of file size.
I will do a follow up post with some more detail and images around this cropping subject later in the week, with full and cropped examples from both bodies, along with some more behavioural shots of this bird.
Sadly, the plum tree that it was sat in is far from photogenic with the 'clutter' behind the bird. I got the ladders and the cutters out today, so if she should make a return, then I can now get a much cleaner shot.