Oh, we've done that; it says see ThrustLimit page in FMS!! More interesting is it adds a caveat that FMS figures are only valid if two ADC's are functional, but gives no advice on setting cruise thrust if you lose an ADC. Good game!
To answer the original question though, on my aircraft the answer is - it depends. Since we have flat rated engines GA N1 may or may not take the temps over the normal limit. If they don't, then there is no limit. If they do then we are time limited