Tribes is more CPU intensive probably because of the extra optimizations it has to make to output to OpenGL.
How much did you pay for that? A 9500 Pro is a much better card in that price range that can get you a lot better fps in most games and the image quality is far better. Anti-Aliasing is much better as well, and also doesn't slow it down tremendously like the nVidia cards do. The Ti4200 is also a Directx7 card, meaning any game that uses DX8 or DX9 enhancements will not show. The ATi cards up from 9500 fully support DX9.
However, if you want something that will overclock, by all means, get a 9600 Pro. The only thing is that they only have 4 rendering pipelines and 1 texture pipeline which is exactly half of what the 9500 Pro has. This makes for some lackluster performance between the two. But, it can overclock like a beast and may outperform it. All up to you, but I recommned going with ATi on this one.
Oh, and btw, nothing new about the 4200's. It is old technology.