It's always interesting in this type of discussion to see how well the industry has beat into a photographers head, that a CCD can really shoot anything but base iso. Excepting being a sensor plus enabled Phase One back, I don't believe by increasing ISO on a CCD, you gain (no pun intended) anything. The readout on a Phase is the same, it's just a metadata writing that shows you set the iso higher.
This has been shown to be true with many tests, I have read both on this site and others, where a 50 iso sample is compared to a 200 iso sample and basically the image will look the same, either with the 50 sample way underexposed, or vise versa.
So I ask again for the experts, does a real "higher than base" iso really exist on a CCD MF back, besides moving to sensor plus, where you do see a definite improvement, still not sure it's really a higher iso, but it's sure 4:1 pixel binning. So with a good lens, you can get a good iso 800 image from a IQ180 albeit it's a 20MP file, thus it's not really a result of a higher iso, due to the loss in 3/4's of the resolution.
I fully understand with CMOS, you can actually increase the "gain" of the chip via the higher iso settings. But with CCD, you best case is maybe 1 step from base, thus on a 50 iso chip, you might increase to 100 iso, but that's not going to do much for a wedding in low light or natural light.
If anyone has information to prove that CCD's in a MF back really can write a high iso file, say true 400 or 800, I would love to see it, as I have never found anything to show this.
Paul