Yet another F10 auto ISO question

Sorry if this has been discussed before, but is there any difference between the Natural Light mode and Auto mode with the flash turned off? I know natural Light mode will go up to ISO 1600 and AUTO only 800, but apart from that is everything else the same?

The reason I ask is because the AUTO ISO setting on my F455 was very reluctant to ramp up the ISO even in dark conditions (except at the tele end). It would do 1/10 second exposures at ISO 100 instead of pushing it up to 200 or 400 to avoid blurry pictures (which I would have preferred).

I got the F10 as a replacement as the description of Natural Light mode seemed to be exactly what I wanted, but it seems quite apparent now that it is TOO eager to push it up to 1600 at the drop of a hat.

However, if AUTO mode will happily push up the ISO to avoid camera shake, but not push it as far as ISO 1600 (which I want to avoid using if at all possible as it's a bit too noisy), then this seems like a better setting for me.

So , in case I've lost you in all the rambling, the question is: Will AUTO ISO mode push up the ISO to avoid camera shake or will it be very reluctant to do so like the F455?