Thanks to rep and Cap787 for the golden advice. It has really lifted my spirits.
A question for Cap787 : the POH uses LRC for OEI so at FL230/240 the TAS goes from 405 to 415 as the weight increases from about 70T to 76T, which might make a difference with the SGRs. How can I be sure about using 415 TAS as you said ? Appreciate more input.