Remeber that 737 that had ice on its engine probes and went into the Plotomac (spelling??).
Those guys set the required EPR but due to faulty indications didn't have anywhere near the required thrust.
For this reason its always a good idea to know what sort of N1 indication you'll get for a given EPR and temperature, so you can tell if there is a problem.
Cross-checking engines is good, but remember if one engine is indicating wrong there's every chance that the other one will be doing the same.
On A/C I fly we use JT9D and RB211, the JT9D has a nice chart (marked guidance only) called "Nominal N1%RPM Take Off". The RB211 only has a chart for Go-Around N1% in alternate EEC mode, but I guess it can still give you an idea.