Or, perhaps he just wants a new camera. If he is still shooting with a T2i then it seems pretty obvious that he isn't just rushing to buy the latest and greatest.
It mystifies my as to why as soon as someone posts a question about buying a new camera that others feel they just have to provide that person with a lecture on how to spend their money. Do these same people lecture their neighbors when they hear they are thinking about buying a new car or a new TV?
It's their money. They get to decide how they spend it.

All good advice so far. As far as wildlife, 400 is where one would want to reach. Both cameras meet this requirement. You didn't indicate if either has IS so I will assume no IS. This means that the long 600 would be harder to steady, and many times may search as far as focus is concerned, when shoot distant objects at the 600. I am sure the focusing has improved since my Olympus SP-550, but it can be an issue. I would pick the larger sensor especially if the pixels are bigger which I suspect they are. Even though I shoot with a 4/3rds camera, there is a point that ISO in low light, and the width of the depth of field, may not meet your needs. The larger sensor should give you a higher acceptable ISO and a narrower depth of field. All in all, looking at all brands (in your price range first, the other requirements second), trying them out at the store, and/or renting the finalist cameras are great ideas.