What's the maximum analog ISO setting on 5d3/6d?

[Marsu42]

What's the highest iso setting that result in an actual measurable improvement for stills shooting over selecting a lower value and underexposing? I know on digic4 it's iso 3200, everything above is just pushed, but for recent models it seems to have gotten more complicated and there seems to be a difference between 5d3 and 6d sensors.

This is a quote from the Magic Lantern dev Alex who's on 5d3 and usually knows what he's talking about: http://www.magiclantern.fm/forum/index.php?topic=9458.msg92000#msg92000

There seems to be 4 categories of ISOs (according to how they behave internally):
a) the ones that can be configured via CMOS[0] (on 5D2: 100-1600; they may be different in photo vs lv; the dual iso module uses this one as max iso)
b) the ones that use digital gain, and you can undo that gain via ML digital ISO controls (on 5D2: 6400); this is used for tricks like gradual exposure, hdr video...
c) in-between (maybe this is also hardware but it has some secondary amplifier path)
d) max ISO that can be applied via exposure override in LiveView

... and he goes on with this interesting statement:

For practical purposes, I consider the max useful ISO to be 1600. The higher ones are not any cleaner (maybe up to 0.5 stops), and the price to pay is a large amount of clipped highlights.

 

[bdunbar79]

I believe the 1Dx's highest analog is 6400.