Ecto - I doubt anyone is qualified to make guesses about 'which protein would be worst'. I truly dont think it's something to be worried about.
Firstly, most of these studies are done in short lived animals. No-one really knows what kind of effect a high protein diet will have on a relatively long-lived animal like humans.
Secondly, I was talking to a friend about this article. He works on the evolution of song in crickets (c.f. Jiminy in Pinocchio). It turns out he has done some dietary studies with his populations and his words were as follows:
"Yes, the ones in the low-protein diet groups lived longer, but the ones on high protein grew faster and got a hell of a lot more action from the lady-crickets. So I know which one I'd choose".