Many VariCam users choose to set the native ISO to 5000 and then use negative gain to set the sensor to 2500-3200 ISO. This creates a very clean, robust image, which some prefer to the 800 ISO native.
Anyone who would like to demo a VariCam LT can shoot me a PM. It's really a great camera.
I used the negative gain feature extensively on a recent shoot. Anything over 1600 would have a base of 5000. Its a really useful feature.