I remember going to the Fast Food Exhibition at Brighton Centre way back in the late 80's. The Donner Kebab a new trend on the market I spoke to a chap selling the equipment and the idea.
He had about 8 different sample of Donner on the go, all had differing tastes. He said that there were over 150 different recipes for a donner.
I'm fairly sure that most outlets would be selling C grade especially in today's financial whole. We used to have a shop in Brighton that we'd make special trips to because of the quality of its meat, but it has sadly disappeared now.
Curiously, I once tried one of those cheap and nasty microwave versions and it had a flavour reminiscent of the old style Donner, I was very surprised.