Here's a few more. #1 and # 2 are pulled back 5 stops and #3 is 3.5 stops (note the significant increase in IQ).
It's pretty cool actually because it's one less thing to worry about if you intend on editing them anyway. They are roughly what I would expect at higher ISO's in terms of IQ.
Actually, for scenarios where you need the best IQ and lowest noise, this is probably a very safe way to shoot.
These shots were performed on the X10 but I reckon I would get the same results from using a base ISO of 800 on my D7000 instead of 200.
Take the wedding situation.
Sometimes you will be at 200, 400, 800, 1600, 6400 so on an so forth.
If you shoot at 6400 in a 800 scene, the noise is already there but you could always shoot at 800 and then pull back to a 6400 exposure.
pull back 800 to a 1600 exposure and the noise increase is minimal, reduce a 6400 shot to a 1600 scene and possible IQ loss from dynamic range reduction is possible.
So it is good in the way that you know if you underexpose "that shot" you don't need to worry about setting it up again.
The downsides (major one) is that every RAW file will need to be processed to correct exposure...which is not the best way to manage time.
Conclusion; probably fair to say due to the time it takes to bring exposures up in each shot, I wouldn't use it for weddings etc...but it's nice to know just how much range the lower ISO numbers have in terms of pulling back exposure!
Bottom line: you can pull back a ISO800 shot 4-5 stops but you'd be lucky to get any movement on your upper ISO numbers.
Images:
#1
#2
#3