Their is know absolute when it comes to this. The best method is to try and play the disc.
That aside, anything in the "red zone" is a pretty good indiciator of problems.
Here is a general set of guidlines (subjective--but most should agree) , A good inicator of a problem is PI higher than 280, PIE higher than 4 on a liteon (greater than 8 on benq 1620). If you get any PO's, your in big trouble!!! With jitter, i look for less than 10% avg and less than 12% max. Also, run a transfer test and look for a smooth read.