Have done the search thing and all it done is confuse me a bit

What i'm after is what is the max safe egt for a td42?
temps taken pre turbo.
Some people are saying 600post turbo and some 600 pre turbo.
I know to expect temp drop on post side so which is the right one(temp) so to speak.
Know i should be playing it safe but when i'm hauling arse up a big hill passing a big b-train i want to know when i really need to back off and when its still all good.
Thanks in advance
Mike