Have experiened this before:
i) if you buy the 450D, it looks good and does perform well in good light conditions. However, after buying it, I was a bit embarrassed because the speed was slow, if you are taking pictures in rapid succession, like a birthday party, or events. Even with in-built flash, the speed tripped me. Picture quality was acceptable. Like other people here, have to sell the 450D.
ii)the 40D is a larger and heavier camera, but better image quality. Speed was much better, and picture quality? very much better...even when hand held, the picture quality is better and good in night light conditions. Many of the clubsnappers here attest to that.
You may wish to rent the 40D (there are hiring companies in Singapore; you need only an IC to do so, and advanced payment). Try it and see if you like it.
There are now many second hand 40Ds on sale here in the buy and sell section, and also the 450D. If you buy new, you will lost quite a lot of money, even if you sell after a few weeks. Why don't you go to Canon showroom in Vivocity, and try (get an SD card for the 450D try out, and a compact flash card for the 40D). That is another way to try.
Hope this helps.
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read
www.photography-xylec.blogspot.com for beginner's photography