The original poster of this thread, pm'd me, and asked if I would be satisfied with the 7D if I only had one camera body for an African safari.
I cannot answer that with a simple, succinct answer for several reasons. First of all, the lenses are more important than the body used, so start with first rate glass. If you cannot afford good prime L super telephotos, then rent them. Do not do without good glass.
The body is of lesser importance than the glass, but the speed of AF and the high ISO noise levels are determined by the bodies, and this will matter quite a bit.
Is a 7D much preferable to the OP's 40D? Absolutely!! But if all I had was a 40D could I get some good images with good glass? Absolutely!
But not as many, or as good, as I would with a 7D. As I said earlier, you really do want two bodies at a minimum. As for 20 x 30 inch prints, one can do that easily with good, sharp properly exposed files from a 40D. I have several 16x 24 in prints from a 40D sensor.
Like with great lenses, if you cannot afford a first rate body, rent one from Borrow Lenses or one of the other vendors. Get it a week before you leave, and practice shooting birds in flight, so that you know how to optimally use the Autofocus, with a single AF point. Do not be offended if I am stating the obvious to you, but lots of folks really seem to think autofocus is up to the camera and let the camera choose the AF points ( this won't work out very well with running wildlife ) , and not a user skill. When you can keep a single AF point on a bird in flight diving for fish, then you can be sure you can follow a lion hunting with a single AF point. -
The Autofocus system on the 7D is orders of magnitude better than the 40D's AF, but the AF of the 7D takes a bit of learning to use most effectively. This is even more true with a1DMk4 or a 1Dx.
So yes, if I only had one body, I could get by with a 7D. Would it be my first choice, no, it is now 2-3 years past its prime). I am not being snide here, I still use my 7D for a great deal of my images, despite owning "better" ( superior technically ) cameras like a 1DMk4, because a 7D is very capable, smaller, lighter, handles easily, and I know it like my own skin. The high ISO files are noisier than a 1Dmk4 or a 5DMk2, but so what, at 100 or 200 ISO who can tell the difference. I stated in my previous post about my images, most viewers cannot distinguish them on the basis of the camera body they they were shot with.
One other big factor in your images will be the quality of your drivers and your guides. Will you have a driver who will get you close to your quarry, and will they do it so the lighting is where you prefer it? Or will they just drive up so you can see the critter, but you have to look over the heads of those in front of you in the Land Rover? Will you be allowed to get out of the vehicle and shoot from the ground. Getting low down on the ground can really improve your shots, but being afoot in lion country is something one wants to have good guides along for advice and awareness. -
Will your outfitter get you out before sunrise, and will they stay after sunset, or will they only shoot between 9am and 5 pm?? The big cats do a lot of their hunting in those hours when the sun is below the horizon. Shooting sunrise shots in the dark afoot, with lions roaring in the background will keep you awake and on your toes... Skip breakfast in the morning, eat brunch after shooting, snack and sleep mid day, and go back out for the evening and come back after dark and have supper.
Have fun, and there will be times when you cannot get great images, so just put your camera down, and smell the grass and the animal dung, and feel the sun on your skin, and realize your dream really has come true.
I thought if I was very, very lucky after I retired, I would only go to Africa one time in my life.
But I found that one time is not nearly enough. Not nearly.
The 5DMkIII could be rented, and do very nicely in Africa, even though the reach is less than the 7D's. You do NOT want a 5DMk2 for wildlife in Africa. It is a fine studio camera, but the AF is not up to wildlife in my hands, anyway.
This frame is from a 7D