Something to remember is that 'stock VID' is not very precise, in the sense that on some cards it's just enough to run the stock clocks, and on other cards it's well above what's really necessary. Cards in the latter category are likely to OC quite a bit better on 'stock VID' because it's basically kinda overvolted to begin with.
I've had fermi's where the stock VID was barely +12.5mV over what was needed for stability at stock clocks (my current cards came at 975mV and are barely stable at 962mV), and one that was 62.5mV over what was needed for stock clocks (I had a 480 that came stock at 1063mV but was actually okay at 1000mV).
So I wouldn't read too much into what you can do at 'stock' VID. I would look at what clocks others can do with the same amount of voltage, and keep in mind that there's a wide range of 'normalcy' ... i.e. if the average person's card can do 900MHz at 1000mV (for example) you're likely to find that most people are going to be able to do 900MHz at somewhere between 950 and 1050mV.