I want the FMC input data to be as accurate as is reasonably possible.
I suggest it is time to consider increasing the, IMHO, rather ludicrous low ICAO standard pax/baggage weights. It could well be that on a full 189 seater a/c you could be 2 tonnes heavier than the load sheet tells you. If all male, full baggage at 20kgs, it will be much more.
Regarding the CRZ MAC, it seems some companies allow you to insert the actual number, others forbid it and stay with the default 5% (B737NG) for a safety buffer. Going up to absolute max alt and reducing to 1.2g if no turbulence is forecast is really taking TEM management to the limits. The forecasts are made hours in advance by computer models and differ depending on the meteo centre who made them. Their accuracy is unreliable. I say this because I've been through areas of forecast turbulence with nothing, not even a cough. If that is the case then the forecast of no turbulence must also be questionable; although the met forecasts in all cases e.g TAF's etc. seem to be always pessimistic. I thought we were in the risk avoidance business.