Well, my forte was building, installing and servicing them rather than questioning the experts on food quality retention at -10 vs -50. I'm guessing it is negligible, as it's been the norm for at least 25 years. I do know that it takes 6 to 10 times the energy consumption to keep a given cold storage room at -50/60 than at -10, and that the most important quality issue by far is how quickly the food can be frozen. It is the same with the tropical fruits I work with now. For example, every hour sooner we can cool a fresh picked pineapple from field temperature of 95F, to 45F (without freezing it) gives 1 to 2 days longer shelf life later in the market.