Well the scoop that I use for her food is by no means accurate - but I'd guess it holds about 1-2 cups - but certainly not over 2 cups. The food she is on is a pretty good food - so It's not like I'm having to feed a lot because the food is just filler, she does also get dog appropriate table scraps too - so maybe that's why she does so good on that amount of dogfood.
I have to exercise her quite a bit to keep her from getting too plump. She has always been plump and lazy... unless you take her for a walk on leash or I take her to the barn with me - she just basically lies around... she has lots of energy when we do something exciting though - but playing in the back yard - or running around the house just doesn't amuse her anymore (old age I guess). The vet is always after me to get a little weight off her because of her hip problems (she's never been obese but maybe 5 or so lbs over weight and just generally on the "fluffy" side) - and slowly decreasing the amount of food she was getting finally got us to where we are, and now that she has been coming to the barn nearly every night and coming with me on a ride for about and hour she's finally got a "waist" again
It's really only the shedding that makes me worry about the food she is on now - she looks great, acts happy and healthy - just too much hair coming off her - something has to be missing.
I haven't been able to find any of the food you mentioned at any of the stores around here other than Pet Valu (I think they sell a couple of those brands) And they all sell pets. All the other stores around only have the more heard of brands - nutro, Iams, Eukenuba... etc. all of which have corn. I think I'll just go to Pet Valu and buy the Performatrin Ultra.
She is due for her check up at the end of the month anyway - so I'll just mention my concerns to the vet too when I'm there, see what he says.