I am looking for a budget, ~$600, dSLR for occasionally shooting birds. Lenses and brand are not very important to me because it will mated to a telescope. What is important - good performance up to, at least, ISO 800 and fast fps. So far, the options available seem to be a used Canon 40D. The soon to be released, Pentax K-x seems ok at 4.7 fps but the buffer is limited to 5 RAW images. Any other options/suggestions that are worth exploring? Thanks.