Before you make a final decision, you should probably go into a shop and handle a 60D. The 60D is not the successor to the 20D-30D-40D-50D lineage. The next step in that path is the 7D. The 60D was an attempt to reestablish a body in between the xxxD consumer bodies and the new xD prosumer bodies. If you have been shooting with a 20D and 1D, I can't imagine you'd be happy with the handling of the 60D being that its smaller than even the 20D. I would go with a good used 50D over the 60D unless you have a huge desire to do video.
As I mentioned before, I had both a 20D and 1D2/1D2N... and upgraded to 50D and 1D3. I was extremely happy with the move in both cases. They are both similar handling to the two bodies you have, yet better in almost every way. That said, a happy medium, which you haven't mentioned, could be to go with a 7D. I know a lot of birders like it... and its more similar to the 1D2 performance, but more the size of the 20D. To me, unless you want to go more in the consumer DSLR direction (smaller, lighter, etc.), the 60D shouldn't even be on your list.