Well all discs will eventually degrade, when is the big question. But if something has more errors and is poorly burnt to begin with, then when it degrades, it will become unreadable before a a better burnt disc would.
However, you ask if the speed affects it. Whether 16x degrades slower than 40x, I have no idea about that, but I doubt the actual burning speed itself can make the disc vulnerable to degrading. I am not 100% sure about this though, as stranger things have happened.