http://www.magiclantern.fm/forum/index.php?topic=10111.0In the first post of that thread, also check the section entitled "Any recommended reading?". The DxOMark site will list the dynamic range for all tested cameras.
ISO 1600 > ISO 3200 may net you 0.4 EV on some camera when you are using standard image capturing. With dual ISO you shouldn't expect to see that result. Each ISO is only half resolution, so you throw away one full stop of (full) midtone resolution, to "
gain" 0.4 EV of
half resolution shadow detail.
When you use recommended settings (100/800....100/1600), since the top couple of stops are generally
white anyway, the resolution loss may not even be noticed. But when you start using extreme settings (100/3200), you're throwing away another full stop of midtone redolution, and this resolution loss is smack bang in the midtones. You probably want all available resolution for the midtones.
Where you use a low base ISO of say 100, the situation is probably even more dire. Here, you probably have your exposure (shutter/aperture) set for the base ISO. Since ISO doesn't effect
shot noise, not only are those last few points of EV only half resolution, but they are also heavy with shot noise.