Hmm... To be honest, I'd have gone for something longer. For European wildlife, I use a Nikon 80-400 VR zoom lens, and mostly towards the long end. A wider aperture will give you a brighter viewfinder image - but I suspect you'll probably end up shooting at somewhere around f8 to get an adequate depth of field; That's what I usually end up doing if I want to get nose/beak and eyes both sharp.

Some years ago we had a speaker at our photo society who did a lot of wildlife photography, and could afford a "big glass" fast telephoto - and when I asked, he said he usually shot stopped down to get the depth of field he wanted.

I used to have one of the old Nikon AF 80-200 f2.8 AF zooms; that was one of their best lenses - really sharp (and to my mind, noticeably better than the 70-200 f2.8 non-VR replacement) - but once I got the 80-400 VR, I hardly ever used the 80-200 - the VR on the 80-400 helped compensate for the smaller aperture, and the bigger zoom range and longer focal length meant I used it more. Eventually I swapped the the 80-200 for the 180 f2.8 AF-D prime lens - almost as long a focal length and a lot lighter.

However, it's quite likely that the f 70-200 2.8 is going to be higher quality than the f4 version - especially since it has a fluorite element. I have a small fluorite refractor and really like the performance. Best suggestion is probably to have a hunt around on the web for photos taken with both lenses and see how they compare. The brighter viewfinder image with the faster lens is another plus, though I've never found f4/5.6/8 lenses to be a problem.