Here is a side-by-side look at the specifications:

http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=casio_exp700%2Ccasio_exz750%2Cnikon_cp7900&show=all

For low light, the p700 would be the better choice.
It has a faster lens rating (when zoomed).

The ISO goes to 640 on the P700.

The P700 was built to compete with the Canon G6 and the Sony V3. That is a pretty nice neighborhood.

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All of the cameras you list take excellent photos.

The two Casio cameras have some important manual controls"
Shutter Priority
Aperture Priority

The Nikon 7900 is point-and-shoot, so it does not have those manual controls. However it is loaded with scene modes.

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