Just to add my 2 cents. Not all pumps are going to shut off at the same time. It depends on the temp and how fast the pumps acually pump the gas. The hotter it is the faster the gas will evaporate. More fumes=less fuel in the tank. I think the dash display is MUCH more accurate than one pump to another.

Also, since my car is an AT-PZEV will the metal tank expand or contract in hot weather more than the plastic tanks? That would have an impact on the amount of fuel capacity.

also, these statements are just my hampster breaking a sweat. Am I wrong?

 

The guage, while much more consistant, still may not necessarily be 100% accurate. When I was at the dealer he mentioned that there was a service bulletin that had some comments about the accuracy/tolerances of the FCD. My guess is that this was in response to people like us who were keep detailed records about their mileage.
As far as the metal or plastic tank, I suppose there could be some contraction and expansion of the tank, but I don't think it would be enough to cause a large difference in capacity.