The Canon 200 f2.8 is excellent. Although I have a 200 f1.8, I would really like to get a 200 f2.8 too. I keep the f1.8 because there are situations where that extra 1.3 stops is crucial, e.g. shooting evening speeches and people at dinner tables. But with high isos performing the way they do today, the size, weight, and cost of the 200 f2.8 are a big advantage. The 200's f2 are generally big and heavy and a pain to bring to a job. I leave mine at home whenever I can get away with it. I recently bought a 135 f2, for jobs abroad because I am tired of flying with the 200 f1.8 in my hand luggage, despite the pure magic it produces. Keep the 200 f2.8 and be happy. If you really need to push the boundaries of low light, then, and only then, in my opinion, is it worth getting one of these f2 beasts. And avoid the Contax, because it's not sharp enough wide open.