The 10D is OLD, even moving up to a 30D would seem like a big improvement!
Forget the whole "professional" thing. There are pros shooting with 1DIV and others shooting with 40Ds, so it is quite irrelevant. Look at your budget, what you want to shoot, and pick the best camera for the job. A camera is a tool just like a lens, nothing more.
While I love the 5D and would recommend it to alot of people it might not be the best tool for you. If you like wildlife you might want to stick to some sort of crop sensor camera, either a 40D/50D/60D/7D or one of the 1D series cameras. Don't worry about megapixels, look at high ISO performance (noise levels) instead. Do some comparing on dpreview.com

