What is the true maximum SOC?

I've been doing some reading on NiMH batteries in the hopes of finding out what the true maximum SOC is. We know that the nominal voltage is 1.2VDC. Just about the entire world agrees with that number.

When searching for the max SOC, I've seen a few different numbers. They are:

1. 1.41 VDC per cell (~8.5 VDC per module)
2. 1.56 VDC per cell (9.36 VDC per module)
3. 1.85 VDC per cell (11.1 VDC per module)

I'm not suggesting that anyone states the NiMH batteries should be charged to these value. Perhaps it's a maximum number before the module explodes. I'm not really sure. That last number (1.85 VDC) is really high and is actually called out in a National Semiconductor datasheet. If the Prius modules were charged to that number, the pack voltage would be ~310 VDC.
Can anyone point me to some type of credible information that shows what the true maximum SOC is

 

My question was pertaining mainly to re-balancing. Using delta peak cut-off is probably preferred but if that option isn't available what would be considered a good voltage to use as a cut-off?