Hi Bart,

Three of us had 500 mm f/4 lenses and 1d Mark IIs.  Another had
a 300 mm f/4 and 20D.  We usually used the lenses with 1.4x TCs
or 2x TCs (on the 1D bodies).  The 300 on the 1.6 crop 20D
is about equivalent to 370 mm on a 1D (1.3x crop) in terms
of field of view.  There were times when I had the 500 +1.4 or
2x when I wished I had on the 300.  Usually there was no time
to change lenses so I just did mosaics.  Here is my first
mosaic: 2 frames on a cheetah, assembled in ptgui:
http://www.clarkvision.com/galleries/gallery.africa/web/cheetah.c01.19.2007.JZ3F
8148-9f-800.html
Of course that only works on still animals.
Everyone got great photos, regardless of focal length.
The bigger lenses helped more for birds.  You'll see as we
post images that we got real close to many large animals.
One day a lion walked past the jeep and the 20D +300 mm recorded
a closeup of just the lion's eyes, but I got nothing as my
500 mm would not focus that close (I did get the lion further out
of course).

I have many mosaics to construct, big animals, birds, and scenics.
It'll take me years ;-).

No one had any issues with not enough memory cards.  I carried
about 74 GBytes of CF cards and did not have to reformat any,
so I returned with 3 copies of all images and 4 copies of most
(I had to delete some from my laptop drive as I ran out of space
on it, but I had 2 usb drives for backup).

I had to clean my sensor once on the 1DII and not at all on the
10D (on which I usually used a 70-200 f/4 IS).  That after 2-weeks
in dusty conditions.

Let me know how the colors and contrast look on the above image.
This is my first processing on a new computer with an LCD,
which is calibrated with a spyder 2, but I'm not completely satisfied
yet (previously I used a sony crt).

Roger