Don't be too caught up on low light performance, I have been using mine every day for the last 4 months in the far North of Sweden, we didn't have sun for over a month and only an hour of lighter sky in the day, temperatures down to -35c and regularly below -20c, the S performed amazingly! Cloudy or shady is never going to be a problem, I do shoot a lot on a tripod when it's dark but normal day conditions are no problem at all.
I haven't tried the zoom so can't comment, it would be very interesting on the 007 when it's released, I would likely never take it off!
This is ISO 800, handheld, jumped out of the car, focussed and shot before they ran off, this is pretty much dark!
This is 4 seconds at ISO 800
This is ISO 400 in a horrific storm, handheld, no light and wide open with the 100
These are just personal shots processed in a way I like, I'm sure others would do things completely differently so please don't take this as me trying to show what the S can do, just what it can do for me.
Get one, shoot with it and enjoy!