low light and zoom

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Hello,
I cannot make up my mind in deciding between several cameras. I keep going back and forth bewteen the Fujifilm FX100, the Olympus X1, and sometime the canon S95.
I would like a large sensor as I do need to take picture in low light, but I am afraid of the fixed lens 35mm.
What could you suggest me to do? I currently own a Canon EOS 33, a Canon EOS 450D (with SIGMA 18-200- and Lumix DMC TZ 20.
Thanks in advance
Xavier