I found a web page several years ago with sensor temp plots for long exposures, for the 1000D and 450D (I recall the 40D also). The 1000D is ever so friendly, the 450D is very similar, if slightly warmer. Peter, the 350D should be similar to the 1000D or 450D +10 - 15 at the outside, without cooling. I'm not sure about 1C though. You may be right.
I guess this can be tested with a cold finger mod by taking a series of 3 min darks with cooling off to measure the dark noise. Then set the cooling to maintain ambient and take another series and measure the noise. Dark noise increases 2x / 6C.
There are number of threads on sites such as cloudy nights about heating of various sensors. Some, such as the 5DMKII run +35C warmer, others are reported to be worse but I forget exactly. It seems to depend largely on the model. I found the 5DMKII, when I had one to be a beast.
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